The 648L is a T47 (47mm x 1.0) left hand threaded standard guide for use when facing bottom bracket shells with the BFS-1 Bottom Bracket Facing Set and 690-XL Oversized Facer This guide is used on the drive side (right side) of the bike - this side of the bike drive uses a counter-clockwise or left hand threading Tap Guide BFS-1 47mmx1 648L