Standard PVC boxes crack during installation when the nail drive forces the box against a stud bow, or fail to hold their position when the weight of conduit pulls on the nail tabs through seasonal temperature swings in an unconditioned garage or basement. 1/2-inch knockouts accept standard PVC male adapters for conduit runs - the most common trade size for residential wiring. PVC construction won't rust or corrode in damp basement or garage environments where steel boxes fail. Type X designation indicates construction for use in fire-rated wall assemblies where a specific box rating is required by code. Nail tabs are integral to the box body - one nail driven straight into the stud face holds position through the pour or the drywall install without spinning or loosening. Round profile fit Stocked at Crofton Lumber and Akron Lumber.