Nylon collar for bottom of SB distributor?

Half the cores I get in the nylon collar is in the engine somewhere. The IPB has the part number. But I throw them out when I get them, at least 50 YO Vinal is a big risk to me. I had metal ones made. Run from the larger 1/2 locking ones they will come loose and also block the oil flow into the distributor shaft.

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