are all unvented cylinder imersion heater bosses the same size the one i am changing is a 2inch thread also the cylinder is just over 2 years old and the 2 elements have gone already they have a sticker telling you on the stat not to adjust it is set at 60 degrees the one i changed i put it down to 50 degrees (hard water area) bearing in mind they are not that accurate plus or minus 5 degrees, these elements are incoloy and the will not change as they are out of guarantee