Our stainless steel bore caps are manufactured by us in Australia, they will not rust.   The standard bore cap will safely fit all bores with a bore casing internal diameter of 220mm or less and this model has a 40mm female BSP thread in the centre together with a slot for cable access.    We laser cut the round plates from 304 stainless steel sheet, brush the face so they are neat and burr free then we attach the 1 x 40mm stainless socket and 1 x 40mm stainless steel tee with a length of 316 stainless steel allthread secured with chemical weld.   The 316 stainless steel eyes are secured with M10 x 40 stainless set screws and the complete unit is then packed ready for dispatch to you.  Strong and much safer & easier to lift out, the stainless steel will not rust and comes with a 25-year warranty.