Today I needed a nut and washer to hold my bike tire. I had one nut already which I was able to lock on there with a 15mm socket & ratchet. So I figured this meant that the nut must be a 15mm and a 15mm washer, if that makes sense? I only had one nut and washer so I took a trip to the hardware store today and I go hunting for that nut & washer. Soon I am overwhelmed with new terminology there were metrics and hex and some other stuff I figured I needed a 15mm so the metric section must be it. I go hunting there but nothing is labeled with mm it's all +1.50 pitch or M8 I don't know what any of that means or how it relates to the 15mm diameter nut & washer. Essentially I couldn't find the right one, an employee showed me what he said was the 15mm nut & washer was but it was way too big so I knew I'd have to go back to do more research. Please explain what pitch means for mm I am very confused here. And if a 15mm socket can lock the nut onto the bike does that mean the nut would have to also be a 15mm nut & the washer?
Thank you
Best Answer
Nuts and bolts start with two options, US or metric. US units tend to be in inches, metric units are typically millimeters. The size of the socket is completely separate from the size of the bolt and nut. The size of the nut/bolt is measured outside of the threads on the bolt, not the nut. So a 15mm bolt measured from the diameter from outside the threads, which would be written M15, could easily require a 30mm socket to install.
The pitch is how steep the threads are. On US nuts and bolts, they are measured according to the number of threads per inch. So a pitch of 20 would have 20 threads per inch. For metric nuts and bolts, it's measured in mm per thread, so a 1.50 pitch will be a thread every 1.5 mm.
The best option, if you can, is to take the existing nut and bolt to the store to find the replacement and ensure you get a proper fit.