Proform 66792 Engine Piston Top Dead Center Locator Tool 
Proform 66792 Top Dead Center Locator Tool; For Spark Plug Hole Use; Included 14mm Adapter; Features adjustable depth; Fit Most Engine. 
It has precise top dead center positioning function, which can easily and quickly adjust and set the equipment, greatly improving work efficiency. 
Simply screw the bolt type piston stop tool into any standard 14mm spark plug hole to quickly locate the top dead center during engine timing. 
The piston stop tool is suitable for camshaft indexing, valve adjustment and distributor installation.