Post 1881 pattern Suffolk Regiment collar badges. The castle of Gibraltar and horizontal key. 13 stones around the archway variant identified in Churchill*, Fig 379. Dimensions are 26.5mm wide, 24.5mm tall.
This badge was supposed to be replaced by the three tower version in 1897 but the new version was not widely worn, the regiment reverting to the two tower type until 1931.

Reference
*Churchill, Colin. History of the British Army Infantry Collar Badge. (Amazon UK link)