Bottom bracket sizing

[dandy1]

Have you got a pic of the side of the crank arms? Or on the inside of the arm, usually by the pedal thread hole they'll be a model number

 

[slackboy]

those are Shimano STX cranks, from 1995ish. The axle length should be 110-113 mm

There is a comprehensive bottom bracket size dbase here:

https://www.sheldonbrown.com/bbsize.html#stx

 

[Tootyred]

Just don't forget to measure the bb shell too. It might be 68 or possibly 73. You dont want to end up with one that won't fit in!

 

[CCMDoc]

I’ve always found Sheldon Brown’s work to be very helpful

Sheldon Brown Bottom Bracket Guide

 

[CCMDoc]

I see Slackboy beat me to it - on the same wavelength I guess.