NOTE, THESE BARRELS ARE FOR THE SINGLE SHOT CONTENDER PLATFORMS, THEY ARE NOT IN ANY WAY FOR SEMI-AUTOMATIC PISTOLS. THESE BARRELS ARE MADE BY SSK IN PA USING GREEN MOUNTAIN BLANKS. PLATFORM: THOMPSON CENTER G1 CONTENDER/SSK50/G2CONTENDER. RATE OF TWIST: 1-14. 810 BULL CONTOUR ANY PISTOL FOREND WILL WORK FINE. FOREND SCREW SIZE/SPACING: 10-32, 3 1/8 Centers. THREADS: Yes 11/16-24 w/Cap. SCOPE BASE: 6 HOLE BASE PICATINNY STYLE FACTORY INSTALLED.