Did u make them ?You may also want to consider a saddle jack for the top of the jack to keep the jack lug from slipping off of the axle. Just a suggestion.
I have two, one for each of my 20 ton air jacks from HF. They work great. I wanted them because my driveway is at a slight negative grade and want to make sure they didn't come off. I also use 6 ton jack stands with the jacks.
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Well, that's my for what ever it's worth?