My girlfriend is 5' tall, and quite a few female friends of mine are under 5'4". If you are less than 5'5" and you are not riding custom cranks, you are probably destroying your knees. Stock cranks only range from 165 to 175 mm. That's bearly a 6% range, while the height of adult humans commonly range by 25%. I'm 6'5", so I am 22% taller than my GF. If i ride 175mm cranks, she should be on 78% x 165 = 135mm cranks. But cutsom triple-ring 135's are upwards of $150, so I made some for her.I used a pair of 170's, chopped and drilled a new hole. These taps worked great. I was a little afraid of getting the threads super straight, to make the pedal axles parallel to the bottom bracket. I just used a hand-held drill, not a drill-press, and VERY cautious eye-balls, and it came out great. Maybe it was luck of the draw. Obviously if you have access to a mill, you'd want to use that.The manufacturer probably has some stupid legal reason to say "not for tapping, only for chasing", but that's fine. The aluminum cranks are made from is usually heat-treated so it is a bit harder than annealed aluminum, still it taps fine. I don't know what the life-span of these taps will be, but if i tap 4 sets of cranks and they turn to mush on the 5th, they will have paid for themselves many times over. They've paid for themselves already actually, after the first set.Good product.