Exhaust valve. 1.22" (31mm) x 3.52"
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!
Note that 12G1316 (Smog-Type), all variations of the 12G940, and the latest CAM head castings all use the following 3.57" long valves.
Early Cooper S valves
If your 970, 1071, or early 275 Cooper S still has the original AEG163 head casting, you must use short, 3.52" valves.