Consistently controlled preload, minimum size and weight, plus speed of installation are outstanding advantages of the collars used on externally threaded pins. A major design consideration was controlled preload built into the fastener. This feature alone has fulfilled a long standing industry need for each fastener to maintain consistently the same controlled preload as the other fasteners used in the same joint. The threaded collar allows for progressive tightening, clamping-up the work prior to final collar torque-off.
The elimination of the wrenching surfaces at the controlled preload results in weight savings of the fastener and wrenching clearances minimized result in weight savings due to more compact fittings and joints. The collar has an elliptical self-locking action. Use of these collar and pin fastening systems provide exceptionally high fatigue life.
The standard collar is tamper proof because it cannot be removed without the use of special tools. The collar’s automatic break-off at design preload eliminates calibrated torque wrenches and torque inspection. There are standard and reduced-hex collars. Among the standard collars, there are basic collars, self-aligning collars and self-sealing collars.
The collar was developed for the HI-LOK™ Fastening System. The wrenching element designed to break-away at a controlled preload was a major design break-through for the airframe industry. It has been tried and tested over time and has proven reliability. Today, all controlled preload collars in the airframe industry stem from this original concept.