3 5/8" X 3 3/8" (93mm X 85mm)   (skirt ink stamp) F.P.L. {Fabbrica Porcellane Lungavilla}   Picture courtesy Dave Dangora

 

FPL stands for the maker "Fabbrica Porcellane Lungavilla" which is a small factory in Lungavilla that started production in 1907 and may still be producing porcelain insulators today.

U number assignment by Bob Berry April 2016.