1.259" (32mm) dia x 3.57 long EXHAUST valve.
Our race valves are produced in EN214N steel and rquire Manganese/Silicon bronze alloy valve guides. They are stellite tipped and use the later narrow, single collet groove and current valve head shapes.
As it is possible, even common, to swap one head for another on 1275 engines, it is quite easy to become confused, or worse yet, confuse the parts-guy when it is time to order new valves! Be aware that if the head has been worked on previously, it may have oversize valves; it may have undersize if seats have been installed. Unless you are 100% sure what is in your cylinder head, it is a good idea to remove a valve for accurate measurement. There are two lengths used (nominally 3.52" & 3.57") three different keepers, (wide, narrow, and three-groove) and many different head diameters! These valves are in stock at Mini Mania!
Note that 12G1316 (Smog-Type), all variations of the 12G940, and the latest CAM head castings all use the following 3.57" long valves.