Set of Adapters and Taps BSA

BSA; British Standard Cycle; is the threaded bottom-bracket standard that's been in service on bicycles since the early twentieth century. The shell is 68 mm wide on most road and gravel frames (73 mm on most MTB), with threads of 1-3/8" × 24 TPI, right-hand thread on the non-drive side and left-hand thread on the drive side. When those threads go bad; paint overspray after a frame respray, corrosion after damp storage, contamination from a stuck BB cup; the chase tap restores them without cutting new metal.

The Set of Adapters and Taps BSA chases both the drive-side (left-hand thread) and the non-drive-side (right-hand thread) BSA threads. The set includes the two thread taps, two adapters that mate the taps to a standard tap handle, and the 1697.4 guide that joins the two taps through the shell. Use with our Handle for Pedal Taps 1695/4BI for the leverage and alignment a BSA shell chase requires.

When to use the BSA chase

• A frame that's been resprayed, where paint overspray has filled the BB shell threads
• A frame that's been stored damp for a winter, where corrosion has built up in unused threads
• A frame where the previous BB has been seized in place and left thread distortion when it was finally removed
• A new frame from a smaller manufacturer where the threads weren't cleaned at the factory

The chase removes only paint, corrosion, and burred metal. It does NOT cut new threads. If the BSA shell's threads are genuinely stripped (the BB cup is cutting new threads into the alloy), the fix is a thread insert or; in some cases; a frame retirement. The chase tap is the cleanup tool, not the repair tool.

Pair with the right handle

The BSA chase taps engage the 1695/4BI handle via the standard square-shank interface. The handle's magnetic-collet grip holds the tap perpendicular to the shell face throughout the cut, which matters because BSA's thread pitch is fine enough that an off-axis chase cuts the thread out of round.

What's in the set

• Two BSA thread chase taps (left-hand drive-side, right-hand non-drive-side)
• Two adapters that connect the taps to the magnetic handle, plus the 1697.4 tap guide that joins the two taps through the shell

Specs

• Thread: 1-3/8" × 24 TPI (BSA standard)
• Sides: left-hand drive (1.3/8" L) + right-hand non-drive (1.3/8" R)
• Compatible with 1695/4BI Handle for Pedal Taps
• Article number: 1697.3 (code 626487); set weight 856 g

Built in Zreče, Slovenia

Unior has been forging hand tools in Zreče since 1919, and sponsors professional road and mountain-bike race teams. The BSA chase tap set is part of Unior's bicycle-specific thread-tool catalog (alongside the pedal-thread and frame-thread chase tools). The thread profiles are sized to Unior's machinist-tool specifications, which differ from generic hardware-store taps; a workshop-grade tap cuts the thread profile to a tighter tolerance, which is what gives the chased thread its clean feel.

Pro tip from our mechanics

The single best test of whether a BSA shell needs a chase: thread the BB cup in by hand. A clean BSA accepts the cup smoothly to the bottom; a contaminated one stops or feels gritty. Spend the 30 seconds chasing the thread before you force the cup. Our workshop hand tools guide covers thread-chase work and the rest of the workshop hand-tool layer: Workshop hand tools every bike shop needs →

FAQ

Does this set cut new threads or only clean up existing ones? It chases the existing BSA threads. The left and right 1.370" x 24 TPI taps clear paint overspray, corrosion, and contamination from a fouled shell so cups thread in smoothly again. If the shell's threads are genuinely stripped, a chase cannot rebuild them; that repair is a thread insert or frame work.

Which bottom bracket shells does it fit? BSA (English) threaded shells only: 1.370" x 24 TPI, left-hand thread on the drive side and right-hand thread on the non-drive side. Italian-threaded shells (36 mm x 24 TPI) and press-fit shells use different standards and need different tooling.

Do I need a separate handle to drive the taps? Yes. The 1697.3 set contains the taps, two adapters, and the tap guide, but no handles. The adapters mate the taps to Unior's 1695/4BI magnetic handle for reamers and taps, sold separately. Unior's 1697-US is the version of this tool that ships with two handles included.

What exactly is included, and can I buy the parts separately? Four pieces: the left and right BSA taps (article 1697.1), two adapters (1697.2/4), and the guide for taps (1697.4) that joins the two taps through the shell. All three articles are also available individually as spare parts, so a worn tap does not mean replacing the whole set.