Studs - Engine Cylinder Head Studs Double Ended Studs fully Threaded Studs. Metric Studs Head Studs Barrel Studs Exhaust Studs Motorcycle Engine Studs. Headless Bolts Steel Studs Used in Cylinder Head to Barrel on Bike & Scooter Engines. An engine stud is often an alternative to a bolt. It is a straight length of steel rod that has threads at both ends. On most engines the most common studs are the 4 for each cylinder barrel and head assembly and those of the carburettor. In the motorcycle engine, the stud is screwed into the crankcase components during manufacture and it is seldom necessary to replace it. However, over time the threads can become damaged or the rod bends. Sometimes it helps the dismantling process if one or more studs are removed. Stud removal is an easy process by adding two nuts, tighten together then unscrew.