Spoke wrenches: what is the right fit?

How do you choose the right size spoke wrench for your wheelbuilding project? Is your choice based on measurements that manufacturers advertise? Or do you use some trial and error?

We put a lot of thought into choosing the right spoke wrench/nipple combination in our workshop. After all, a poor choice could lead to damaging new components, and make an otherwise enjoyable wheelbuild not so fun. 

A good fit between a spoke wrench and the nipple flats will occur when the total clearance from the nipple to the spoke wrench is about 0.02 mm. Given hand tool manufacturers work to clearance tolerances specified by ISO (the International Organisation for Standardisation), or go further and produce products with tighter tolerances (e.g. Stahlwille), spoke wrench choice should be easy. Right? Not always so. Tool wear on the wrench occurs, and needs to be monitored. For example a brand new SW-0 Park Spoke Wrench might be a good fit for a 3.25 mm nipple, however a well-worn SW-0 can become a loose fit on a 3.30 mm nipple.

We use a digital micrometer to take width measurements of our nipples as part of our process for creating product descriptions for each nipple. We see minimal variability in our measurements across the wrench flats, but we still measure at least three randomly selected nipples before reporting an average measurement to two decimal places.

In the real world there are a multitude of nipple sizes with different manufacturing histories and standards. This is the reason why we aim to have a broad range of spoke wrenches on hand in the workshop, to reduce the risk of damaging wheel components.