Cylinder guards were designed specifically as a solution to this problem for commercial property owners. Cylinder guards are fully bevelled outer shield rings to provide an extra layer of protection against prying. The guard makes it virtually impossible to grip even with tools. They are made of hardened steel so that they can’t be damaged by any standard hand tool.
Even if a burglar were to drive a tool into the stile behind the shield ring, they’d have to pull a heavy steel plate through a small round hole. Needless to say, most burglars won’t be successful with this method.
Hence the cylinder guards protect against wedging, prying, drilling, cutting