A clevis shackle is a piece of rigging equipment that has two component parts: the clevis and clevis pin. The clevis is a U-shaped rod or bar of steel that has holes in the prongs. The clevis pin is a bolt that is inserted through the holes in the clevis and can be threaded or unthreaded with a cotter pin. A clevis pin has four different dimensions that are typically measured. The best way to measure a clevis shackle is with a caliper.
Measure the outside diameter of the clevis in the saddle of the bow. The outside diameter of the clevis determines the load capacity of the shackle. The caliper measures four different dimensions: outside diameter, inside diameter, depth and step. You will use the two sets of jaws on the caliper to measure the outside and inside diameters.
Measure the holes on the prongs of the clevis to determine the size of the clevis pin. Use the inside diameter jaws of the calipers to get this reading. The inside diameter jaws of the caliper are the small jaws located opposite the large jaws. You can verify your measurement by measuring the outside diameter of the clevis pin using the large jaws. Record your findings.
Insert the clevis pin and measure from the pin to the saddle of the clevis. Use the smaller jaws to take this reading. Insert the flat portion of the smaller jaws into the opening between the saddle of the clevis and open the jaws until the outside surfaces of the jaws make contact with the inside edge of the saddle and the inside edge of the clevis pin. Write down your findings.
Measure the mouth opening of the clevis. Use the smaller jaws to measure from one inside edge of the clevis opening to the other inside edge. Make sure the caliper jaws are not cocked or you will get an inaccurate reading. Document your reading on the same piece of paper you recorded the other readings.
Make sure you close the jaws of the caliper before making any reading and that means every reading.
Each time you close the jaws of the caliper you must get a zero reading on its display or your measurements will be inaccurate.
Clean off the jaws of the caliper before making any reading if the caliper does not zero out. Dirt and debris can accumulate on the jaws and cause the caliper to give you a larger measurement.
Always check the load capacity of the clevis shackle before using it as rigging. Overloading a clevis shackle causes the shackle to fail. A broken clevis shackle under load can cause bodily injury to any personnel standing close to the rigging.