Jethro, I don't have time tonight to search the old messages, but if you'll do a search on "slip clutch" I'll bet you find more information than you want to read. Basically, a slip clutch usually costs about $100 more than a shear pin and requires a little more maintenance than a shear pin. I don't have a slip clutch on any of my implements and wouldn't want one; no rocks on my place. But if you're going to be frequently hitting rocks, stumps, and such, then the slip clutch may be worth the extra cost instead of frequently changing shear pins.
Bird