This is a Hasselblad extension tube 21. It can be attached between the lens and the body for macro photography. Attach it to the lens first, then to the body. To remove it, detach the body with the lens attached, and then remove the lens. Please be careful, as the shutter will close if you get the order wrong. I purchased this used, so it is not a one-owner item. I am also listing other Hasselblad-related items. Shipping will be via Yu-Packet Post Mini. Instant purchase is OK. Price negotiations are not accepted.