Post-Type Insulator Covers interlock with 1.5” (38mm) Class 4 Extended Lip SU System or Conventional Line Hose. The PTHS for insulators up to 12” (305mm) and the PTHL for insulators up to 16” (406mm) in height. The PTHL cover also has external ribs on the ears which secures 2.5” (64mm) I.D. line hose. Always use clamp pins to secure the device into position.