Black plastic delrin 2 piece reducer bushing for post clamp system. Can be made to fit the 3 size post clamps we make to reduce the diameter to fit post sizes that fall in between the sizes we offer of 1.5", 1.75" or 2.0" diameter post clamps. Please measure your post and let us know what size you will need by email. There are too many different sizes to list here. Pricing the same, no matter the size.