Buyers compare strap by break strength, but a strap never breaks in the middle. It fails at the joint. A 1,000 lb strap with a poor joint is a 400 lb strap. Here is how the common joints compare and which one belongs on which load.
The four joints
| Joint | Strap | How it works | Joint strength (share of strap break strength) | Consumables |
|---|---|---|---|---|
| Friction weld | PP, PET | The tool vibrates one strap layer against the other until the plastic melts and fuses | About 75 to 85 percent on PET, 60 to 75 percent on PP | None |
| Crimped metal seal | PP, PET, steel | A metal sleeve is crimped over both layers with a sealer | About 60 to 70 percent, lower if the crimp is uneven | One seal per strap |
| Sealless (punched) | Steel | The tool punches interlocking tabs through both layers | About 70 to 80 percent with a full, clean punch | None |
| Buckle | PP, polyester cord | Strap is threaded through a wire or plastic buckle and held by friction | About 50 to 60 percent; can be re-tensioned | One buckle per strap |
Those ranges come from industry rules of thumb and our own pull tests on a bench; your results depend on the tool setting and the strap. The point is the order, not the decimals: a good weld on PET beats a crimped seal, and both beat a buckle.
Friction weld: the default for cartons and pallets
Every Rockcub machine for plastic strap welds: the RCV2 handheld, the RCV3 tabletop and the RCV9 arch. No seals to buy, no seals to run out of on a Friday afternoon, and the joint is consistent because the tool controls the weld time, not the operator's wrist. Two things make a weld fail:
- Dirty or wet strap. Oil, dust and moisture stop the layers fusing. Keep coils off the floor; our strap storage article explains why.
- Wrong weld time. Too short and the weld peels; too long and melted strap squeezes out and the joint thins. Set it per the strap thickness and check the first joint of the day by trying to peel it by hand.
Metal seals: when you have a manual tool
Crimped seals are how manual PP and PET kits work: tension with one tool, crimp with another. The joint is acceptable for light cartons but it is slow, the seals cost money on every strap, and a half-crimped seal looks fine until the truck hits a bump. If you are still crimping more than a few dozen straps a day, the maths usually favours a welding tool within a year of consumable cost.
Sealless steel: no clips, no stock-outs
For steel strap, the sealless punch joint is what our RCV4 and RCV5 make. It removes the seal as a consumable and as a failure point, provided the punch goes fully through both layers. Our steel strapping how-to shows what a complete punch looks like.
Buckles: for things you need to open again
Buckles are the only joint you can loosen and re-tension, which is why they suit tarps, bundles that get added to, and loads that settle over days. They are the weakest joint on the list and should not be the primary restraint on a freight pallet.
Picking by load
| Load | Strap | Joint |
|---|---|---|
| Cartons, parcels, bundled paper | PP | Friction weld (RCV3 at a station, RCV2 if you move around) |
| Pallets, lumber, mixed freight | PET | Friction weld, RCV2 |
| Steel pipe, coils, bricks, hot or abrasive loads | Steel | Sealless punch, RCV4 or RCV5 |
| Anything that has to be re-opened | PP or cord | Buckle |
Test your own joints
You do not need a lab. Weld or seal a loop of strap, hook it over a forklift tine and hang a known weight from the other side. If it holds twice the heaviest load you ever put on one strap, you are fine. If the joint lets go first, change the setting before you change the strap.
Questions? Phone +1 (562) 203-3004, Mon–Fri 9am–5pm Pacific · support@rockcub.com