Most people believe that the tang inside a valve lock is what actually holds the valve spring retainer and spring in place while the engine is running. This is not the case. The cross-section of material in the tang is not strong enough to withstand today's open spring loads of 1000 pounds or more! The sole purpose of the tang is to temporarily locate the lock, retainer and spring relative to the valve until the taper of the retainer can nest around the outside surface of the lock. This creates a "collet" effect that binds the two together. The more spring force exerted on the retainer (as the valve opens), the more force applied by the "collet" effect to keep the retainer and lock in place.
With the emergence of valve sizes other than the standard 5/16", 11/32", and 3/8", it is important to make sure the valve locks match the valve size. There are a couple of small items to check to see if you have the proper size valve locks for your valves. There should always be a small gap between the two halves of the lock when they are properly positioned on the valve stem. If the two halves butt up against each other without a gap, the valve locks are for a bigger size stem. If the locks fit tight to the stem and leave a gap between the middle of the lock and the O.D. of the stem, the locks are too small for your valves. All locks should be checked prior to final installation to make sure that they are the correct size. With such small parts, the possibility always exists for mixed or mis-boxed parts.