This is a standard concave or cupped guitar strap button as used in most electric guitars at both ends of the strap and on some acoustics at one end of the strap.

Mounts using one screw and felt pad, supplied. 14mm diameter. 

Concave Gold Plated Strap Button Please email sales@jellyfishaudio.com with a list of items you wish to order and we will send you a link to make a secure Stripe payment. Price: £1.49