The other day I bought a new fill cap (green) for my diesel deck
fill. Both my deck
fill and cap are plastic (non-metallic). Although the new cap appeared to be the right size, it just wasn't threading well and I didn't want to force it, so I returned it and bought a new o-ring. The 1-1/2" o-ring is just slightly bigger than the old one, but appears to seat ok in the fill neck. Its just not tight around the cap neck.
Did deck fills go metric or something? My boat
was built in 1991, so did the sizing change over the years?