SnapOn Battery Insert - ctb4187 - ctb4185 (NiMH 3.8Ah) 18v SnapOn battery pack insert. Just unscrew your old pack, take out whats inside, and put the new pack in its place. For SnapOn Ctb4187 and ctb4185 snapon battery packs 18 Volts, 2.2Ah NiCd or 3.8 Ah NiMH options simple instructions included, T10 torx Security bit required