Ultradyne UD Lightweight Butt Stock Spacers are compatible with the UD Lightweight Butt Stock to give the consumer an additional .25a ^2 LOP (Length of Pull) per spacer. Simply remove the butt pad screws and insert the desired amount of spacers (up to four total) to fit the shooters needs. Made from a durable Nylon 12 material, you gain a sturdy spacer while remaining lightweight.