Quicklinks - safety limits?

Nick Goldsmith wrote: I have broken a bunch of climbing rope with hardware store quick links.  Mostly 5/16ths links that are rated 1750lbs working load which means their actual strength is 3 times that or something thereabouts. Only that strong when the collar is screwed shut with a wrench.  I have also broken rope with  1/4 in hardware store link that was severly abused non my snow plow for several years before testing.  I would bail on 1/4in link any day but certainly would prefer a real biner. 

You've "broken rope"?