On thin plastic stock you can cut a piece of block plastic, I used a 3" piece of bulk nylon round stock i had on hand and shaped it to just about match the interior curve of the hollow stock, then measuring carefully and clamping it temporarily in place I drilled a pilot hole for the wood screw type threads on the swivel. Then I lightly coated the block with polyurethane sealant where it would contact the interior of the stock to make up for any inexactitude in the fit. Once I stuffed it back into place it was pretty easy to screw the swivel in catching the block inside the stock. It held up until I sold the gun a few years later and, as far as I know, is still good.