Frog Shields are precision machined and anodized, 6061-T6 aircraft aluminum, replacements for traditional caster wheel spacers. Frog Shields fit over the wheel bearings to protect them from damage due to debris, water, hair and anything else NASTY. Over time buildup of grit, hair and gunk will chew up and crush your bearings resulting in reduced rolling efficiency. Frog Shields are designed exclusively for Frog Legs brand aluminum caster wheels in sizes from 3" to 6". They will also retro-fit to Frog Legs existing wheels made in prior years. You will love how easy it is to keep your wheels clean. No wiping, no tweezing, no NASTY.