Jeffrey Mine Insulator
Reprinted from "INSULATORS - Crown Jewels of the Wire", April 1969, page 13
by Howard Banks
Out of the damp, dirty, dark, long since played-out holes that men have
carved in the mountains of Colorado have come a beautiful (and quite valuable) collectors
No, not gold; but, originally, a cheap glass instrument used to insulate
low voltage power lines for lighting the inside of mines.
The collectors item is the very scarce JEFFREY MINE INSULATOR. Embossed:
SPECIAL MINE INSULATOR / JEFFREY MFG. CO. /COLUMBUS OHIO/
PATENT SEPT. 25, 1894, this insulator is one of the rarest and most sought
after of all threaded insulators.
The pin hole for the mine insulator goes clear through the insulator. The
wire groove is in the center of the insulator. The patent for the mine insulator was
issued to David N. Osyor. Osyor was given the right to the patent by Joseph A. Jeffrey,
president of the Jeffrey Manufacturing Company. The Jeffrey Company produced all types of
It is unknown who made the insulators for the Jeffrey Company; however, due
to the drip points on the Jeffrey mine insulator it could be speculated that the
insulators were made by the Hemingray Company.
The pins for the mine insulators were specially equipped with a small
drainage tube to remove water from the open upper end of the pin. The pins were so arranged
that the insulators hung downward yet the pins were driven into the walls of the
At the present time I have located only about twelve JEFFREY MINE
INSULATORS. There is an unknown number of other mine insulators including
unembossed, no drip point types, types with no drip points embossed only
MINE INSULATOR, porcelain unembossed types, and types embossed HEMINGRAY on
one side and No. 95 on the other side. These have drip points.
The Jeffrey's, possibly not the rarest, are by far the most desired due to
the unusualness of the name. Mrs. Gerald Brown of Two Buttes, Colorado mentioned
in a letter to me that she felt that the Jeffrey's are equal in value to the
BOSTON BOTTLE WORKS or the E. R. W. She states that it is hard to figure their
value in comparison to unthreaded types because collectors with unthreaded types
prefer to trade for other unthreaded types.
It might be noted, however, that there are far more than a dozen U.S. Tells
or MULFORD & BIDDLE'S known. Many collectors value the Jeffrey far more than
these insulators; and, of course, many other collectors value the Jeffrey's
less, preferring other insulators.
I have located two major varieties of the Jeffrey's : embossed correctly in
relation to the drip points; and embossed upside-down in relation to the drip
points. The embossing is the same in both varieties except that those embossed
upside-down lack periods after MFG. and CO. and SEPT. whereas the other types
have these periods. This indicates that the Jeffrey's were made from at least
If you have one of the Jeffrey's, you should consider yourself very
fortunate. These would be the "prize" of any collection.
I would like to learn just how many mine insulators embossed with the Jeffrey
name are known. If you have some or know of some body who does, I would
appreciate hearing from you.