The APR AN Bolt Length Gauge accurately shows the proper length of the AN Bolt required when original bolt lengths are unknown and helps to choose the proper length for new holes drilled during installations of modifications. The AN Bolt Lenght Gauge shows 5 lenghts for each of the 8 AN Bolts starting at 1/8" through 7 7/8" in increments of 1/8" (a total of 275 sizes)
To find the length of the AN Bolt rotate the top disc of the computer until the material thickness is shown in the top selector window. To the left of the window find the AN Bolt diameters (AN-3 bolt is 3/16", AN-4 is 4/16" diameter etc.) Select the bolt length in the window opposite the desired bolt diameter to be used.
The selector window shows the proper length when using two thick flat washers. If two thin or one thick flat washer is used, reduce the bolt length one size. If material thickness is in 1/16", 1/32" or 1/64" round to the nearest 1/8".
AN Bolts and proper installation are required by FAA regulations
