Square Tube Plugs

Two measurements: outside dimension and wall thickness. Both sides of a square tube should be equal. If they are not equal, you have a rectangular tube and need rectangular tube plugs instead.

Step 1. Measure the outside dimension

Use calipers or a ruler across one side of the square tube, outside edge to outside edge. Measure both sides and confirm they are equal. Match to one of the 16 available sizes for these plugs.

Step 2. Measure the wall thickness

Use calipers at the tube end, or calculate: (outside dimension minus inside dimension) / 2. Many square tube plug sizes offer multiple wall thickness ranges. Choose the range that contains your measured wall thickness.

Step 3. Confirm both match

Both outside dimension and wall thickness must fall within the listed range. A 25 × 25 mm plug sized for 1 to 2 mm wall will be too loose in a tube with 0.5 mm walls and will not fit a tube with 3 mm walls.

Corner alignment: when installing these plugs, align the plug's corners with the tube's corners before pressing in. Square profiles require rotational alignment that round profiles do not. If the plug feels like it is catching on one side, rotate it slightly until all four corners line up.

Same press-fit installation as round tube plugs, with the addition of corner alignment. Square tube plugs must enter the tube with corners aligned to corners. Once aligned, the flexible ribs compress and grip all four interior walls.

What you need

• The correct square tube plug matched to your outside dimension and wall thickness
• A rubber mallet (recommended for larger sizes and thicker walls)
• Clean, dry tube ends free of burrs or sharp edges

Installation steps

1. Inspect the tube end. Remove any burrs, sharp edges, weld spatter, or debris from the inside corners. Square tubes accumulate more debris in the corners than round tubes do.
2. Align the square tube plug with the tube opening. Match corners to corners. The flat head faces outward. The ribbed body faces into the tube.
3. Press the plug into the tube by hand. Apply even pressure across all four sides. The flexible ribs compress as the plug enters, then expand against the inner walls.
4. If needed, tap the plug head evenly with a rubber mallet. Apply force to the center of the head, not to one edge. Uneven force can seat one side deeper than the other.

Removal: pry gently from one corner with a flat-head screwdriver. The PE body flexes without breaking. Square tube plugs can often be reinstalled if the head and ribs are undamaged. On square profiles, starting the pry from a corner provides the best leverage.

The same four problems as round tube plugs, adapted for square geometry. The National Wood Flooring Association (NWFA) recommends protective measures on all furniture legs, and these plugs provide that protection on hollow square metal legs.

Floor protection

An open square tube end puts four sharp metal edges and four sharp corners on the floor. That is eight points of potential floor damage with every movement. Square tube plugs replace all eight with a smooth, flat PE head that distributes weight across the full square area. On hardwood, laminate, vinyl, tile, and polished concrete, the PE surface slides without scratching. Unlike leaving metal edges unprotected, the plug eliminates the damage at the source. For additional PA6 scratch protection, apply a square self-adhesive furniture pad to the plug head.

Tube sealing and moisture protection

An open square tube collects moisture, debris, dust, and insects. On steel tubing, trapped moisture causes internal corrosion that weakens the frame from the inside out. Square tube plugs seal the opening completely. The ribs grip all four walls, and the flat head covers the entire cross-section. Moisture stays out. The tube interior stays dry and clean.

Noise dampening

Hollow square tubes resonate and amplify contact noise just like round tubes. The flat metal edges ring against smooth, hard floors. Square tube plugs fill the tube opening with PE, absorbing the vibration. The flat PE head replaces the metal-to-floor contact. In restaurants, offices, conference rooms, and schools where metal chairs move constantly, every sealed tube end reduces the cumulative noise level. Press-fit these plugs that silence the rattle.

Finished appearance

An open square tube end looks unfinished. The hollow interior is visible, and any internal rust, weld marks, or manufacturing residue shows. Square tube plugs cover the opening with a clean, flat PE head that signals a complete, intentional design. Available in black, gray, and white, the plugs match or complement any frame finish. On commercial furniture, retail fixtures, and display structures, a plugged tube end communicates professional attention to detail that an open end does not.

Square tube plugs are designed for any hollow square furniture leg or structural member that needs a finished, sealed, protected endpoint. The 16-size range covers virtually every square tubing specification in the furniture and fixture industry.

Ideal applications

• Dining and side chairs with square metal legs (20 × 20 to 30 × 30 mm is the most common range)
• Tables and desks with square tube frames (30 × 30 to 50 × 50 mm)
• Commercial and restaurant seating
• Office furniture: desks, conference tables, shelving units
• Retail display fixtures, point-of-sale racks, showroom furniture
• Industrial and workshop tables (50 × 50 to 100 × 100 mm)
• Garden and outdoor furniture with square metal frames
• Gym and fitness equipment frames

Not ideal for

• Rectangular tubes (unequal sides): use rectangular tube plugs
• Round tubes: use round tube plugs
• Oval or ellipse tubes: use oval or ellipse tube plugs
• Solid square bar stock (no hollow interior): use square end caps instead
• Sizes larger than 100 × 100 mm: contact Business Solutions

Match the plug shape to your tube shape. Every shape uses the same PE construction and ribbed grip mechanism.

Round

26+ sizes, Ø 10 to 80 mm. 7 head styles.

View round tube plugs →

Square ← You are here.

13 × 13 to 100 × 100 mm. Black, gray, white.

Rectangular

32+ sizes for unequal-sided profiles.

View rectangular →

Oval

Oval cross-section profiles.

View oval →

Ellipse

ellipse cross-section profiles.

View ellipse →

Half-Oval

D-shaped cross-section profiles.

View half-oval →