Back when I did HO, I've used the UK N Scale (1:148) assortment of pipe fitting casting by PD Marsh. They have two types large (which scales to 12in UK N, or ~13" in 1:160) bore and a medium (9in or ~9.73 in 1:160) bore. But for my current structure project, such is just too big.
For this effort, I'm flexible in size that scale at or below 5", and ideally would like to find two sizes. Perhaps something that worked with my supply of 1/32 tubes and rods (~scale 5") as well as with 0.015 wire (~scale ~2.4")
Might anyone have an alternative source?