Adding a spring-loaded, locking ball in the cylinder crane is standard practice on Smith & Wesson K, L and N Frame revolvers, especially when installing a bull barrel. Steel fixture holds the crane secure and in proper alignment for drilling; makes it virtually impossible to mislocate the hole or drill at the wrong angle. Comes complete with No. 30 drill bit, .125" diameter locking balls, springs, and staking punch. Mfg: Power Custom SPECS: Drilling Fixture - Steel, blued finish. 1A 1/2" (3.8cm) long, 1" (2.5cm) wide, 2" (5.1cm) high. Includes No. 30 cobalt drill bit, (20) 302 SS locking balls, 20 springs, and staking punch. Designed for K, L and N Frame yokes only. Crane Ball & Spring Refill - Contains