Lockbolt Tools 101: C6L, Magna-Grip, and Joints That Do Not Loosen

If a joint has to survive years of vibration without loosening, a lockbolt is usually the right fastener. It is worth understanding why, because lockbolts get specified into designs and then set with whatever tool is on the cart.

How a lockbolt works

A lockbolt is two pieces: a pin with locking grooves and a collar. The pin goes through the hole, the collar goes on the tail, and the tool does two things in one stroke. It pulls the pin to develop tension across the joint, then it swages the collar material down into the locking grooves. Finally the pin breaks at a designed pull groove.

The difference from a blind rivet is meaningful. A blind rivet upsets a soft body against the back face - clamp load is modest and varies with hole fit. A lockbolt develops high, repeatable tension and then mechanically locks it in place. There is no thread to back off and no spring element to relax. This is why you find them on trailer frames, rail cars, agricultural implements, truck bodies and shipping containers.

C6L vs. Magna-Grip

Two systems cover most of what our customers run.

C6L

A pull-type lockbolt with a relatively narrow grip range per part number. Because the grip range is tight, the set is very consistent - which is exactly what you want in a repetitive production joint where the stack thickness does not change. Our 202HC1 (3/16") and 202HC1L (3/16" extended) nose assemblies are the C6L pieces.

Magna-Grip / multi-grip

Designed to cover a wider range of material thickness with one part number. That flexibility is worth a lot in repair work, field service, and mixed production where you cannot guarantee the stack. It also means fewer SKUs in the bin. Our multi-grip nose assemblies are the 202HM1 (3/16"), 202HM2 (1/4") and their extended L versions.

Important: the nose assembly determines the system. A tool set up for C6L will not properly swage a multi-grip collar. If you run both, keep both nose sets and label them.

Sizing the tool

Lockbolts need far more force than blind rivets of the same diameter, because you are swaging a collar rather than upsetting a soft body.

• ZT2318H - 5,000 lb traction, vacuum, 3/16" and 1/4", ships with your choice of one nose piece.
• ZT2318HA - same 5,000 lb tool without a nose piece, for shops that already have assemblies.
• ZT2318HK - the kit: 5,000 lb, pulls both 3/16" and 1/4" in both C6L and Magna-Grip. The practical choice for a shop that runs mixed work.
• ZT3213 - 7,050 lb, 3/8" vacuum lockbolt tool, no nose included.
• ZT2420HS-3 - split type with a nine-foot hose, when the power unit needs to sit away from the work.

The split-type deserves a note: separating the cylinder from the pulling head puts far less weight in the operator's hand. On overhead or repetitive work that is a genuine ergonomic win.

Common mistakes

Hole size. Lockbolts are less tolerant of oversized holes than blind rivets. If the pin can move in the hole, you lose the shear performance you specified the lockbolt for.

Grip range. Too thin a stack and the collar swages into the wrong groove; too thick and the pin will not break where it should. If you are seeing inconsistent pin breaks, check stack thickness before you check the tool.

Squareness. Off-axis pulls produce partially formed collars. Use an extended nose to get square access rather than angling the tool.

Getting set up

If you are specifying lockbolts for the first time, tell us the material stack, the diameter, and whether the joint thickness varies. That determines the system, the collar, and the tool. Call +1 (330) 677-1330.