The type 2 or 7 ones seem to be the right thing, but I am rethinking this since the ones I was really interested in were $14 each and I need 6 of them. I am wondering why I cant just take your advice and put rubber under the 4x4's I have them bolted to. So, since i have plenty of rubber for that purpose, why not just try that first. If I decide later it is inadequate, I will re-visit McMaster.