Abstract: In the combination of a railroad rail and a rail-piercing gun having a support area extending across the tread of the rail, a gauge is provided which includes a rail-end stop bearing against an end of the rail, and an elongated saddle bar connected to the stop, and having in a side away from the tread of the rail a plurality of seats spaced a distance equal to the desired lengthwise spacing of fish plate bolt holes to be formed by the gun, of a length and depth to accommodate closely the gun support area and of a height from the tread to locate the gun at the desired position heightwise of the web of the rail. In the use of the gauge, the gauge is placed on the rail, the gun is seated in a seat whereby the saddle bar is held in position laterally of the tread, the gun is moved away from the stop end of the gauge until the stop engages the end of the rail, a hole is formed with the gun, the gun is moved to another seat and the process is repeated.