Sheet metal clips and crimping tools: how open seals join plastic strap

The sheet metal clip is one of the simplest parts in a strapping system: a short strip of thin steel, formed into an open channel. Yet a poorly matched clip can let a plastic strap joint slip. The clip, the strap and the crimping tool make the joint together, and each has to suit the other two.

This guide explains how open clips work with PET and PP strap, which dimensions define a clip and what to look for when checking crimped joints on the line.

Open clips, closed seals and buckles

Plastic strap can be joined in several ways. Friction welding melts the two layers together with no added part. A wire buckle holds the strap by threading and friction. Metal seals join the strap ends by being crimped around them.

Metal seals come in two broad forms. An open, snap-on type is placed over the overlapping strap ends during or after tensioning, then closed by the sealer. A thread-on seal must be threaded over the overlapping ends before the tensioning tool is applied; Signode’s seal overview lists that style for steel strap. Open clips suit manual work on plastic strap because the operator can tension the strap, place the clip over the overlap and crimp it without threading anything.

The same overview makes a distinction worth remembering. On steel strap, joints may be notch type, where the tool cuts the seal and strap edges to form a mechanical interlock, or crimp type, where the seal and strap are pressed into wavy crimps. Plastic strap joints use crimp-type seals or buckles. A crimped joint on plastic strap holds by friction, which is why strap thickness and surface matter so much.

What defines a clip

A clip is more than its nominal width. When identifying or replacing one, record:

Dimension or feature	Why it matters
Nominal strap width	The clip must fit the strap without excessive side clearance
Sheet thickness	Affects how the clip deforms and how much grip it can develop
Clip length	Determines how many crimps the tool can form along the joint
Profile and edges	Influences how the clip wraps the strap and whether edges cut it
Inner surface	Some seals carry a grit coating inside to raise friction; a plain and a coated clip grip differently
Finish	Affects appearance and corrosion behaviour in storage

Two clips described as 16 mm can differ in every other row. If your current joint performs well, keep a sample of the accepted clip and record these features, so a repeat order can be checked against it.

How crimping works

A crimping sealer closes the clip around the strap, then its jaws press the clip and strap into a series of crimps. The deformation locks the layers together. The tool has to suit the clip width and length, and its jaws have to be in good condition.

Manual sealers, often paired with a separate tensioner, suit low and medium volumes. Combination tools and machines that feed seals from a magazine are also used with plastic strap. Either way, the joint depends on three things being right together: a clip of the correct size, strap of the expected thickness and surface, and a tool that forms complete crimps.

ASTM D3950-16 covers nonmetallic strapping and joining methods together. Its abstract notes that seals and buckles may be steel with zinc, black iron oxide or equivalent protective coatings, and lists joint strength among the properties addressed where applicable. That is the right frame for a buyer: a clip has no strength of its own in isolation, only as part of a tested joint.

Matching clip, strap and tool

Before approving a clip, check:

• Strap width and thickness. Measure the strap actually in use rather than relying on the label.
• Strap surface. Embossed and smooth strap present different surfaces to the crimp, so approve the clip on the strap you will actually run.
• Tool model and jaw condition. A worn sealer can produce shallow crimps with a good clip.
• Crimp pattern. Sealers differ in the number and spacing of crimps they form; the clip length must suit the tool’s pattern.
• Joint position. The clip should sit on a flat face of the load, not over an edge.

Spotting a poor crimp

A quick visual check at the start of each shift, and whenever clips, strap or tools change, catches many problems:

• Crimps that are shallow, uneven or missing along part of the clip.
• Strap visibly sliding out of the clip after tensioning.
• Clip edges cutting into the strap.
• A clip that is wider than the strap, leaving it free to twist.
• Cracks in the clip at the crimp lines.

If any of these appear, stop and check the combination rather than adding a second clip. A double clip can hide a mismatch that will show up again under load.

Making a change safely

Treat any change of clip supplier, strap grade or tool as a joint change. Run a short trial on real loads, record what was used and keep the accepted samples. Our sample approval guide explains how to capture the decision, and our comparison of clips and wire buckles helps when a different closure is being considered.

Matching clips, strap and crimper

YAKU’s sheet metal clips are intended for PET and PP strap, with strap, clip geometry and crimping tool to be checked as one system. To pair them with strap, see the PET strap page. Performance values are on request; share your strap reference and tool through the enquiry page.