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Porcelain Spool and Knob Insulators

Spool or knob insulators typically have a non-threaded hole in the center for mounting and a wire groove around the outside.  These insulators are used for dead ending a communication or power line and are often found mounted on racks on the sides of buildings where the wires enter the building.  They are also used for wire transposition where two or four spools are mounted such that the wires can tie off and cross.  There is currently no hobby numbering scheme for porcelain spools.

Some smaller porcelain spool styles as follows:  Left to right

  • Chocolate Brown inkstamp marked "1968 - SAFEGUARD / MADE IN CHINA"

  • Unmarked brown

  • Brown recess embossed "PIERCE"

  • Dark brown embossed "P.P. USA No. 24"

  • Unmarked brown

  • White recess embossed "USA"

  • Brown recess embossed "JOSLYN / B"

  • Brown embossed "D in a square"  (Square-D Corp.)

  • Unmarked brown


Some colorful spools as follows - Left to right:

  •  Unmarked cobalt blue spool

  • Mottled gray recess embossed "LM in a triangle" (Line Material Co.)

  • Unmarked large yellow spool

  • Brown spool recess embossed "JOSLYN / 101"

  • light blue recess embossed "PIERCE / 1609"

  • Unmarked mottled blue-green

  • Yellow spool incuse marked "PP" (Porcelain Products)

More colorful spools as follows - Left to right:

  • Unmarked cobalt blue spool

  • Unmarked small yellow spool

  • Unmarked large mottled blue spool

  • Unmarked large gray spool

  • Unmarked light blue spool

  • Large cobalt spool incuse marked "LM in a triangle / 642R" (Line Material Co.)

Porcelain spools from outside North America - from left to right:

  • Unmarked cobalt blue spool

  • Tan spool incuse marked "MADE IN ENGLAND"

  • Small blue spool from Australia incuse marked "KP"

  • White spool with green glaze stripes

  • Unmarked blue-gray spool

  • Unmarked small green spool

  • Unmarked light gray spool

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