By James Price

Inventors in the 19th Century sought patents for improvements to tools to make them perform better and sometimes, with more precision. Such is the case of G.L. Holt of Springfield, Mass. who on June 29, 1875 was granted U.S. Patent No. 164,999 for a more precision way to hold bits in a brace. The Barber Shell Chuck, patented a decade earlier, had seized a big part of the market and was quickly making button and lever chucks obsolete. Holt took the idea of a shell chuck and promoted it to a higher level. He promoted the concept that a bit which could be screwed into a brace chuck would eliminate wobble in boring. His patent called for a threaded brace tang that screwed into a brace chuck but the patent drawing did not illustrate a brace. I found such a brace in 1963 with one bit and since then I have aggressively attempted to build a set of bits to accompany the brace. The bits you see in the first photo were added to my collection one at a time. I will never find one each of all the tools that accompanied a Holt brace but I have successfully assembled what is probably the most complete set known to date. The bit tangs have left hand threads and a double taper on top of the tangs. A shell chuck on the brace is rotated left and inner threads draw a bit into it and the taper on the tang seats in a vee notch in the brace frame. This retains a bit on the precise longitudinal axis of the brace and the tang in the notch prevents the bit from slipping in the chuck. I use this brace and it’s bits on occasion when I do some very precision boring. It performs exactly as the inventor envisioned. If you find one of these Holt braces at a yard sale, you can sell it for a handsome profit to an advanced collector.

This photo shows my Holt brace and all the auger bits for it I have been able to find.
The shell chuck has left hand internal threads that draws the threaded bit into place.
The bit tang has a double taper that fits in a notch inside the shell chuck.
Specialized Holt bit tangs could be purchased from the manufacturer. This bit has one of the Holt tangs forged welded onto an Irwin solid-center bit.
A special adapter could be purchased that allowed standard bits to be used in a Holt brace.
Many kinds of boring and drilling tools were offered with Holt tangs. On the left is a countersink, in the middle a metal drill bit, and a large English English center bit is on the right.
This is G.L. Holt’s patent drawing of 1875.

This is a copy of a period advertisement for Holt braces and bits.


This is a copy of an article in an 1883 Scientific American periodical describing Holt braces and bits.