They last for as long as you want, depending on how bothered you are by the slow, gradual reduction in sound quality. If it's very important to you, you'll want to change them every few months, but I've had mine for almost a year because I'm not that bothered, and they're an extra expense. I can definitely hear the reduced quality now though. I don't think it's bad for your records unless the needle's actually dmaged, but I'm not 100% sure about that.

as a rough guide, depending on the weight, 3.5g lasts about a year, add a couple months for less weight, take a couple months off if u use more weight i have ortofon concordes on 2.75g and quality is as good as when i bought them in november 2001 and i spin an average of 4-5 hours a day, every day

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w: www.luketerry.com

Shit! I must be doing something wrong I broke one with in 3 months and the otherone is getting a bit worn.
I have been a bit vicious with them a few times though.