Petrek 3G / GPS-4 Silicon case (Replacement part)

The Petrek Silicon case is designed to fit most small to medium-sized collars and is compatible with large collars when used with the large collar adaptor strap (sold separately).

It is engineered to break and snap off when put under pressure in tight situations. 
Thus, if your mischievous cat or dog become trapped under a house or over a fence the Petrek unit will break off rather than stay on.