This is another, somewhat lighter green MIVA A 318 CA. Compare in size to a normal CD 155 for size reference. This is a three-part glass insulator, cemented together, markings on top surface, and CA designates a wider top groove for larger gauge aluminum wire. Not yet cleaned up, but it still looks great! Voltage rating is 18 Kilovolts. A Miva A-320-CA (20KV, 3 part) is listed as CD 377.2, this one is just slightly smaller.

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 refers to "Medium Voltage" and A to "Alto" or High Voltage, different times, different electrical standards and definitions apply. FWIW, B as in BT2CA would mean "Basso" or Low Voltage.

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 derivatives closer than either CD 375 (M 312 CA or 6310) or CD 377 (A 320 CA). As far as I know there is no listed CD for the A 318 CA.