Stronghold is universally recognised as our most trusted maximum security brand. It symbolises our 240-year heritage and stands for the very best in British made locks. Tested and approved to the highest Sold Secure Diamond and Gold standards.â¢Maximum security Stronghold D-lockâ¢Sold Secure Bicycle Diamond and Secured by Designâ¢Ultra-secure restricted key system prevents unauthorised duplication of keysâ¢Precision CNC machined solid steel â¢Over 500,000 key differs â¢Recommended for e-bikes and all high-end bicycles â¢Made in Britain