For valves with 10 mm stem -- All 356 and 912 three-piece case engines -- This guide is Std Size: 14,07 OD x 73,00 length. Guide is US-produced, made from superior phosphorus-bronze with provision for valve seal. You need 8 per engine.

This is a Standard Size guide with an OD of 14,07 mm (.554"). Length is 73,00 mm.

Once installed, these guides have to be reamed to size to accommodate the stem diameters of the valves you are going to use. Note, modern-day valves slightly differ in stem diameter and in material from original valves.