This vacuum hose joiner is 1-1/2" OD X 3" Long and made out of aluminum.  Aluminum will not rust and is lightweight.  This connector is specify for use with hose cuff that are ridged and cannot stretch like standard vinyl hose cuffs.  Many shop vac use stiffer hose cuffs, so if you want to add some hose length, you will need to purchase this style connector instead of the plastic style.  All the plastic connectors are ever so slightly larger than 1.5" OD so if the hose cuff is rigid, they will not work.