The ST51 uses the "monkey on a stick" mounting system which is similar to that of the DeArmond Rhythm Chief. A clamp fastens behind the bridge which supports the volume pot and an arm which suspends the pickup over the top. The pickup itself is somewhat thicker than the modern Stimer reissues (about 3/8"). Guitars with low clearance may not be compatible.
There's nothing like the sound of these vintage Stimers! There's a richness, especially in the high end that's missing in the reissues. Here's a rare chance to party like it's 1949!