mtnbke

It's a handy tool for determining the bolt circle diameter (bcd) of chainwheels. What is easily discernible ie. measurable is the linear distance between chainring bolt holes center to center (c-c). However, chainrings are sized according to the "circle" size of the bolt holes NOT the linear distance between two bolt holes.

It's a great tool to carry to a bike swap to get great quality rings like TA cheap. There are many bcd "sizes" that can't be discerned just by looking with the eye test. Only a broke fool walks around a swap with vernier calipers and a slide rule to convert bolt hole distances to bcd. If he can't afford the tool he can't properly afford to stock up on chainrings at a swap, regardless of his measuring and math skills.

Any shop that can't afford a BCD gauge is wasting productive time. A lot of bike mechanics in this industry are stoned out of their minds, and can't effectively make the calculation manually, at any given moment. It's just the right tool for the job to ensure a quick, convenient and failsafe way to ENSURE identifying the actual BCD standard. Destitute and covetous internet trolls who can't afford bike tools will post as apologists that it's not a "needed" tool. Most of them are tools. Any tool that prevents a mechanic from wasting valuable productive time grabbing the wrong size chainring out of spare stock and bringing that to the repair area wasting time/steps is cheap insurance. The primary operational expense of a repair department is labor. The customer pays for neeeded parts/bits. Think of the BCD gauge as being a quality tool to keep the mechanics productively efficient. Considering how low paid most wrenches are and the poor skill level and quality of their work, versus the value of the repair ticket to the shop, it's a necessary tool. Think of it as a Poke-yoke or "idiot proofing" of making sure the right size gets identified, the FIRST TIME. Allowing the shop to leverage that $12/hr wrench into billing more repair invoices in the accrued payroll period.