A mid-sized, three part, 18KV rated power insulator in dark green, unlisted in GIFONA. The CA designation indicates a wider top and side cable grooves to accomodate larger diameter aluminum wire. I'll post a new, closer-up photo soon. This one is not listed in GIFONA, but all indications point to it being in the CD 376 family. The slightly larger 20KV rated A-320 is a CD 377.2 This one is slightly larger than a CD 376 (Miva M-315-CA or Fidenza 6315, but not as large as a CD 377

These apparently were marked with A 318 CA and M 318 CA, M standing for "Medium Voltage" and A for "Alto" or High Voltage. Different times, different engineering standards...

The dimensions are top skirt: 6 7/8 inch diameter; middle skirt, 5 7/8 diameter; base diameter 4 4/3 inches; and overall height 5 1/2 inches. This matches CD 376 and its derivitaves closer than either CD 375 (M 312 CA, Fidenza N°10-B or 6310) or CD 377 (A 320 CA). As far as I know there is no listed CD for the A 318 CA.