Bottom Bracket Facing Guide BSA

The 1699 BB facing tool needs a reference for its cutting axis. The shell's own threads are that reference, but only when the facing tool has something to grip the threads with. The 1699/4BSA facing guide is that grip: a paired set of threaded inserts (one for the drive side, one for the non-drive side) that screw into a chased BSA shell and present a flat, coaxial mounting surface for the 1699's frame.

What this piece does

The 1699/4BSA is a matched pair of BSA-pitch (1.37″ × 24 TPI) threaded inserts, stamped BSA-L and BSA-R. They thread into the BSA shell with the thread direction matching the corresponding side: BSA-L into the drive side (left-hand thread), BSA-R into the non-drive side (right-hand thread). Once both are seated in the shell, the 1699 facing frame passes through them, and the cutter rides coaxial to the bore as it cuts each face.

The guide is the piece that translates the shell's internal thread geometry into an external mounting reference for the cutter. Without it, the cutter has no clean coaxial line to follow; with it, the cutter's path is determined by the shell threads themselves, which is the geometric reference the bearings will eventually live on.

Compatibility

• BSA-threaded BB shells (1.37″ × 24 TPI)
• Mates with the Frame for 1699 Bottom Bracket Facer 1699.2/4
• Part of a complete Bottom Bracket Facing Tool 1699 setup

Specs

• Thread: 1.37″ × 24 TPI (BSA)
• Pair: BSA-L (drive-side, left-hand thread) and BSA-R (non-drive-side, right-hand thread)
• Function: threaded reference inserts for the 1699 BB facing tool
• Tightening: use the 1699.5/4P facing-guide wrench
• Made in Slovenia by Unior

Includes: One BSA-L guide insert, one BSA-R guide insert.

Made in Slovenia, since 1919

Unior has been forging hand tools in Zreče since 1919, and is the official technical partner of multiple World Tour and downhill teams. The guide is the geometric pivot of the BB facing operation; it takes the shell's own thread spec and converts it into the cutter's setup reference. Building the guide to that geometric responsibility means tight thread tolerances and flat outer faces that mate without rocking. The 1699/4BSA's working surfaces are the kind of small precision detail that decides whether the facing operation produces a square face or a slightly cocked one.

Pro tip from our mechanics

Chase the threads before mounting the guide. The guide threads in by hand; if it doesn't seat by hand the threads aren't clean, and forcing the guide will damage either the guide or the shell. Run the BSA taps through first, blow the shell out, and then thread the guide in by hand until it bottoms against the shell face. Tighten with the 1699.5/4P guide wrench; finger-tight isn't enough to hold the guide square through a cutting operation.

Both guides should bottom against the same plane on the shell faces. If one side leaves a visible gap and the other doesn't, check whether the shell faces are out-of-parallel by enough that the facing operation will produce uneven cuts on each side; sometimes the answer is to start the facing pass and let the cutter equalize them, and sometimes the answer is to investigate why one face is so much shorter than the other before cutting.

The BSA-shell prep walk-through covers the chase-then-mount-guide-then-face sequence in order: Frame prep: threaded bottom bracket shells →