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That's a good idea, use a double plate.For a slip on, you need two pieces. Take some 3/4 plate and duplicate the holes, but cut the slot out a different side. Best to drill one more 1/2 inch hole through both (where they both have meat) and bolt the two in place so you can pull the other three bolts out without loosing stuff. The collar flange will bend far too easily if you don't back it up like that.