Bottom Bracket Tap 1697 BSA

BSA (1.37″ × 24 TPI) is the threaded BB standard our mechanics see most often on North American benches, and the 1697 is Unior's complete tap set for chasing it. Two thread directions live inside a BSA shell: right-hand on the non-drive side, left-hand on the drive side. Both have to cut cleanly before a cup torques in without binding. The 1697 ships as a paired chasing tool that runs both sides at once, so the drive-side and non-drive-side taps stay parallel through the shell.

What the tool does

The 1697 is the assembled BSA BB tap set: paired tap cutters in the correct thread directions, locked into a guide frame, driven by twin handles working simultaneously. Running both taps at the same time keeps them coaxial through the shell, which is the difference between threads that come out parallel-and-clean and threads that come out skewed enough to bind a cup at install.

Run the taps through the shell after the frame comes back from paint, after a frame swap, or any time you want to confirm the BSA threads are clean enough to torque cups in without binding. The taps don't cut new threads in unthreaded material; they chase existing threads, removing paint film, anodize buildup, and minor thread damage.

Compatibility

• BSA-threaded BB shells (1.37″ × 24 TPI)
• All steel, aluminum, and titanium BSA shells; carbon shells with threaded inserts
• Pairs with the Bottom Bracket Facing Tool 1699 for shell facing in the same setup

Specs

• Thread: 1.37″ × 24 TPI (BSA)
• Pair: one right-hand tap (non-drive), one left-hand tap (drive)
• Drive: twin handles, modular handle pattern shared with 1694, 1698, 1699, and Taps T47
• Made in Slovenia by Unior

Includes: Right-hand BSA tap cutter, left-hand BSA tap cutter, twin handles, guide frame.

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. BSA is the threaded standard that most Unior tool-purchase decisions land on for North American shops; the 1697 is the front-line tap set for the BB thread the bench sees first and most often.

Pro tip from our mechanics

Cutting oil on each tap before it enters the shell is the cheap insurance against galling. Run both handles simultaneously, slow and steady, with both mechanics watching the swarf coming off; chunky chips mean the tap is dragging and you need more cutting oil and a quarter-turn reverse to break the chip. The swarf wants to come off as a continuous ribbon.

Then there's the drive-side direction trap: BSA drive-side is left-hand thread, marked L on the tap, and it cuts when you turn it counterclockwise from the drive side. Forcing it the wrong direction on a paint-fresh frame is how taps get bent or shells get galled. Read the tap stamp before you reach for the handle.

Full BSA-shell walk-through (chasing threads first, then facing the shell, with feed control and chip-pattern diagnostic): Frame prep: threaded bottom bracket shells →