Large sized, ribbed black rubber horn bulb 115mm diameter with brass ferrule and 15mm horn tube hole. This rubber horn bulb can have the end opened out if too small using a rough round file. It has a removable plug in small end under the ferrule to aid adjustment and fitting. To fit - remove brass end ferrule and push onto the horn tube, remove the end plug and push this on to the tube (easing with washing up liquid helps) then push the round bulb on to this (it locates into a moulded ring). Finally, pull the brass ferrule back into place over both parts of rubber bulb and the part should fit snugly.