BSA Meteor Mk1 Leather Piston Washer.

Leather Cup Washer for BSA Meteor Mk1 & Mk2

Also fits early Mk3

Warning - replacing your air rifles mainspring may increase its power making it illegal. Redbeck Shooting Supplies would recommend that you seek manufacturers advice or a professional gunsmith before attempting to alter your rifle, and that you always check your rifles power using an accurate chronograph to ensure you stay within the law.