Bollard Post Sleeves Easily Slide Over Existing NPT Pipes To Help Eliminate Maintenance. Bollard post sleeves resist fading, rusting and cracking to ensure long life. These post sleeves are made with high density polyethylene to provide effective use outdoors. Smooth surface exterior measures 64H and can be trimmed for an exact fit. Constructed from 1/8 thick high density polyethylene. Includes Two 1W red strips for enhanced visibility.