How to connect 2 4X4 posts: full guide [with pictures] (2023)

Most DIYers and carpenters have a few ideas on how to connect wood using glue, nails, screws, and nuts. However, when it comes to joining parts for structural purposes, we admit that we need help. How to connect 2 4×4 posts is a common question on many websites, so we decided to put together a helpful guide.

To connect 2 4x4s, use a half lap joined with construction adhesive, two steel plates, and four to six 1/2" or 5/8" thru-bolts. Posts supporting roofs or decks should be 20" to 24", other structures should be connected 6" to 10" along center line.

In this guide, we'll identify when to splice 4x4s and explain several current methods that are code-compliant. We will also identify and explain the most robust way to join 4x4. By the end of your read, you should understand how to join 4x4s end to end and when it is acceptable to do so.

quick navigation

  • When to connect two 4X4 posts together?
    • extend posts
    • Repair
    • build long skates
    • post to beam connection
  • How to Connect 2 4X4 Posts Together - The Most Popular Ways
    • Butt joint with steel plates
    • half turn joint
    • dowel joint
    • Butt joint with hollow tube insert
    • Modified half round joints
    • Tapered Interlock Scarf Gasket
    • Column cover/base supports
  • What is the strongest way to join 2 4X4 wood studs?
  • conclusion

How to connect 2 4X4 posts: full guide [with pictures] (1)

When to connect two 4X4 posts together?

There are many reasons to put 2 4x4s together. Making a longer post, cut very short,fixing a post, construction of a longer part on a skid, and post-beam connections are the most common reasons.

extend posts

Adding a privacy barrier or roof shelter to a deck is a frequent reason for doing this.handrails or deck postshigher. Extending fence posts to increase fence height is another reason to lengthen 4x4 posts.

Two other reasons are based on transportation and availability issues. Transporting and connecting two 8-foot sections is easier than transporting one 16-foot section, especially if traversing forest trails. Availability of long 4x4s from many small providers is often limited due to low demand, making splicing a necessity.


Wood is susceptible to rot or damage. Repairing a 4x4 is often easier than dismantling and rebuilding a fence, deck, or other structure. Especially if the post is fixed in concrete or supporting other pieces. Figuring out how to keep everything together while the 4x4 is being repaired can be more difficult than the repair itself.

build long skates

Joining 4x4s for horizontal use instead of vertical use is done in a similar way. The orientation of the cuts should maximize lateral resistance and avoid trapping penetrating moisture. Stresses applied to the skid will also affect the type and orientation of the connection. A pulling force versus a downward force affects the joint differently.

post to beam connection

Attaching a 4x4 post to a beam or beam to a post can be done in several ways, depending on the purpose and where the connection is made. Using specialized brackets is a common way to secure parts and hold a butt joint. A mortise and tenon connection will look best, but may not provide the necessary supporting strength due to the dimensions of the wood.

How to Connect 2 4X4 Posts Together - The Most Popular Ways

Carpentry and joinery are ancient trades filled with specialized terminology and tools. A chamfer joint is any connection where two pieces of wood overlap or overlap flush in the same direction of the grain. Connections must withstand vertical and horizontal forces or stresses, so it is important to consider these when choosing a connection. Strength and resistance to compression or tension can be improved with glue, strapping, or plates and screws.

There are manypopular ways to connecttwo 4x4s together to increase their length, some are easier than others. It is wise to check your local codes for requirements and have a structural engineer check, especially if you are dealing with supporting or covering people. Additionally, any cuts or holes in the treated wood should be coated with an end-cutting solution containing copper naphthenate or sulfate.

Professional observation:When using bare or galvanized metal on pressure-treated wood, it is recommended to protect contact surfaces withbituminous love🇧🇷 The tape helps prevent corrosion and seals against moisture. Always use stainless steel clad fasteners or pressure treated dip galvanizedIt will outlast untreated steel fasteners, but stainless steel will outperform them all. If you are near salt water, stainless steel bolts and plates are better than hot-dip galvanized.

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Butt joint with steel plates

How to connect 2 4X4 posts: full guide [with pictures] (2)The easiest way to connect two 4x4s is with a butt joint. Trim the ends to be joined so they are square and smooth. Any angle, however small, can act as a cutting line, and a smooth, flat surface allows for a better connection.

If a 4x4 is being attached to widen an existing one or replace a damaged section, the work should be done where the starting pole is. To join two sections to be assembled together; It can be done on a flat surface such as the floor, platform, easel, or table.

How to connect 2 4X4 posts: full guide [with pictures] (3)There are different lengths, widths and thicknesses of steel sheets or straps to ensure a butt joint. Some are raw steel, others are galvanized, stainless steel, or lined with ceramic or plastic. Plates can be pre-drilled asPlacas Simpson Strong-Tiewith staggered holes to prevent cracking; others need to be drilled for fasteners. Two boards must be used to support and reinforce opposite sides to prevent buckling.

To drill a steel plate for 1/2" threaded rod or screws, mark where the holes should be. Depending on the thickness, drill a pilot hole and enlarge the hole by increasing the diameter of the bit several times. Opposing boards must have corresponding holes for through-bolts.

There should be two screw holes for each connected part. Most codes call for 1-1/2" between the edge of the wood and the screw hole, which doesn't leave much room for offset fasteners on a 4x4.

For through-rods or screws, secure the plate in place with cable ties, make sure the posts are lined up and level, and mark the holes. Remove the boards and drill the posts. Treat the holes with wood preservative, secure the boards in place, put washers on the screws and push them through the holes, add another washer and thread the screws. Check the levels again by fully tightening the screws.

To connect Simpson Strong-Tie (SST) or other pre-drilled boards to 4x4s, align and level posts with boards and fasten securely. Some boards have a set of holes in the midline that can line up with the board and still have enough screw holes.

How to connect 2 4X4 posts: full guide [with pictures] (4)Offset the opposite boards half the distance between the rows of holes, which will make it easier to fix them. Use appropriate fasteners such as SST #9 x 2-1/2”structural connector screwsto fix the plates to the posts.

Follow manufacturer's instructions or structural engineer's recommendations for bolt pattern.


  • Quick, simple and easy to install.
  • good vertical resistance
  • Staggered fasteners prevent cracking


  • weak side strength
  • hard to align
  • not aesthetically pleasing

half turn joint

How to connect 2 4X4 posts: full guide [with pictures] (5)

A lap joint, also known as a lap or half lap, has been used to join lumber in longer lengths for over a millennium. Half lap is a seam that overlaps half the thickness of the pieces to be joined for a less visible seam. Increases wood-to-wood contact for better connection and strength. The joint looks like the seat of a chair with a high, straight back.

To make a half round joint, measure to find the center line of the two pieces and mark the two sides at the end and near where the cut to form the seat will end. Measure from the tip and mark the desired cut length and mark on both sides and pieces. While the depth is always half, the length of the cut will depend on usage and compliance with local building codes.

There are several ways to remove the wood to make the cobblestone; however, lengths and location play a role. A basic hand saw, hammer and chisel, or all three, have worked for centuries. Electric or battery-powered hand saws or reciprocating saws are a modern convenience that can make the task easier. I have seen a good hacksaw do a series of half turns in the same amount of time as a jigsaw and with much more precision.

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If both pieces are movable, place them on horses or a flat surface, measure and mark them. Using the tools of your choice, remove the necessary wood from both pieces to form the seat and bottom of the joint. If a piece is under a platform or still holding a fence or railing, the arm and clearance can determine which tool to use.

Careful and precise measurements and cuts are required so that structural integrity is not compromised. Do not overcut vertical or horizontal cuts or you will create a cutting line.

What the pieces will support and their location will determine the length of the loop. Posts that support roof or deck structures have different requirements than fence posts or mailbox post extensions. A 10" round with six framing screws or three 1/2" or 5/8" through screws will work for a privacy fence, while a 4" to 6" round with 4 framing screws or two 1/2" through screws /2" of 2" will do for one mailbox postage.

Roof or deck pole slices generally must comply with the Code. Some jurisdictions require posts to have a 24" turn with two 18" steel plates to sandwich the center section of the connection. Four 1/2" or 5/8" through screws secure the joint in a slightly staggered pattern maintaining 1-1/2" between the center line of the screw and the edge of the wood.

Another location requires the collar to be 22" long with five 1/2" or 5/8" thru-bolts with washers.Check before countersinking screws as some areas do not approvefor 4×4 structural supports. Screws should be staggered and 1-1/2" from the edge, no less than 3" from the neck ends and 4" between the screws.

Wind loads and other lateral forces may need to be considered when guiding the direction of rotation. A connection with cuts perpendicular to the force is stronger than those parallel to the stress. When butting four corner posts to support a roof framing, it may be recommended to alternate the orientation of the overlap.

How to connect 2 4X4 posts: full guide [with pictures] (6)To further strengthen half lap joints, use a construction adhesive such asliquid nailsor Loctite PL Premium. They are rated for indoor and outdoor use, are waterproof, paintable, and even cure in subzero temperatures. We suggest fitting the gasket and securing it in place and then drilling the holes.

Spread the joint apart, apply the compound evenly, then reattach the two pieces with several through-bolts to maintain alignment. As the screws are tightened, the stickiness of the glue makes the pieces want to be misaligned, making it difficult to fix.


  • Easy to do
  • Very strong vertical and lateral articulation.
  • Excellent long grain to long grain connection
  • resists twisting


  • saw skill
  • Precision
  • Afternoon

dowel joint

Pins from 3/8" to 1-1/4" long can be used to add lateral strength to butt joints. Measure carefully to drill and align 1-4 holes at the ends of each 4x4 and drill the holes 1"-3" deep. Cut dowels 2" to 6" long, sand cuts, glue and tap into place.

Cover the protruding part of the stud with glue or pour some glue into the holes in the tops and push it into the studs. Tap into place with a hammer if necessary.

Similar butt joint reinforcing connections can be made using two to four biscuits inserted into corresponding slots cut into the ends of the 4x4s. Alternatively, cut a matching groove in the top ends and glue into a wood groove. Cleats, biscuits and grooves reinforce alignment and provide lateral reinforcement.

The use of butt joint sockets connecting light-duty poles is often helpful. However, for structural purposes, it is often necessary to join two steel plates with structural connection bolts or 1/2” through bolts on opposite sides of the joint to add more strength as well.


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  • Improve side connection
  • cheap board


  • Difficult to accurately align vertically
  • It can cause a failure to cut

Butt joint with hollow tube insert

A 10" to 24" hollow metal tube, 1" to 1-1/2" in diameter, inserted into a hole drilled vertically through the center of the ends of the two 4x4s to be joined, Provides additional lateral reinforcement. The tube is fixed in the vertical holes with construction adhesive. Two 1/2" through-bolts are inserted into the top and bottom post pieces through holes drilled in the wood and pipe.


  • Improved Lateral Strength
  • less visible connection
  • strong vertical joint


  • Special tools are required
  • Post can twist out of alignment
  • The tube weakens the lateral resistance of the wood.

Modified half round joints

How to connect 2 4X4 posts: full guide [with pictures] (7)There are numerous ways to modify a swing. Some involve elaborate cutting and may even include a wooden pin to secure the joint. The less complex joint retains the traditional parallel and perpendicular cuts and is easier for the novice.

The half turn interlock connection has an additional 'teeth' or spike cut into the end of the saddle behind the turn. The 'prong' has a receiving channel cut into the opposite base of the other post. The two lengths of the posts slide together, so precision is key. The joint is usually secured with construction adhesive combined with 1/2″ or 5/8″ through bolts with washers or steel plate.


  • Strong side and vertical seams.
  • Highly aesthetic articulation


  • high skill level
  • requires more time

Tapered Interlock Scarf Gasket

How to connect 2 4X4 posts: full guide [with pictures] (8)

A bevel or sheer joint is a diagonal joint cut with a slope of 1:8 to 1:12 and is as old as the half-round joint. It is commonly found on beams, flanges, or other horizontal members attached with wood dowels or screws and plates. The bevel joint requires some modification when used to extend a post.

A scarp cut joint has the sharp edges of the slope cut perpendicular to the outside face of the wood or slightly sloped against the scarp. Form a flat end or seat with the long slant cut; It looks like a chair with a high sloping back. The flat end, together with the diagonal connection between the long grains, improves the vertical or compressive strength.

When used to spread skates, the pointed scarf usually has a stepped slope called a hook. The hook adds another opposing plain that lateral tensile forces can "hook" against. The end-to-end or end-to-end hook and scarf may also have a key or notch cut into the corresponding angled faces to allow a wedge to be inserted to lock the joint.

For added strength, apply construction adhesive to cut faces and connect with 1/2" or 5/8" through bolts with washers or steel through plates.


  • Stronger than half-round or butt joints
  • Withstands twists and turns.
  • Strong vertical and lateral connection
  • Ideal for skate or pole extensions.


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  • Measurement precision
  • cutting ability
  • Harder than swing

Column cover/base supports

How to connect 2 4X4 posts: full guide [with pictures] (9)There are different metal brackets and sleeves that can be used to reinforce a butt joint between two 4x4s. 12- to 18-gauge galvanized, powder-coated, or stainless steel post deck/base brackets such as those inSimpson Strong-Tie Double 2x4 Mailbox/Buffer, provide a strong connection. Use structural connector screws, 10d common or #9 1-1/2” stainless steel screws to attach the brackets to the 4x4s.

The length to be extended and its purpose determine whether clamps or brackets should be used. Supporting a mailbox or light fence is more acceptable than using them to lengthen a post to support a roof or deck structure. Using a membrane or bituminous paste between the wood and the metal will help prevent moisture damage and corrosion of the metal.


  • A quick and easy connection
  • some vertical force
  • easy to install


  • weak side resistance
  • not aesthetically attractive

What is the strongest way to join 2 4X4 wood studs?

Joining 4x4s to increase their length can be as easy as a butt joint or as complex and elaborate as a keyed double groove joint. However, some cuts are best executed when the beams can be easily rolled and joint alignment and fit tested. When working on poles under load or limited space, simpler connections are better.

our choice forThe strongest and easiest way to join two 4×4 posts is a glued, faced, and bolted half-round joint.Cutting a half turn into an existing fixed post is easier than all other cuts except the butt joint. The two cuts required per post are simple and doable even with limited space.

One glued, plated and boltedpointed taper joint is stronger than half a turnbut not so easy to cut in a limited space. Although it also has two cuts per 4x4, precise cutting is more difficult. The skill level and the aesthetics of the finished joint influence the choice of connection. A badly sawn joint will not make a strong connection.


The best way to join two 4x4s to extend a post is with a half turn. The simple cuts make it ideal for beginners and professionals alike, and it's easier to do in a limited space. Adding glue, plates, and screws increases lateral and torsion forces to form a very strong connection.

I hope you have a better understanding of how to connect two 4x4s together and which joint will provide the strongest connection. If you find the guide useful, please share it with others. As always, your comments and suggestions are appreciated.

Eugene Sokol

Eugene has been a DIY enthusiast for most of his life and loves to be creative while inspiring creativity in others. He is passionate about renovations, renovations and carpentry.

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