Product Overview
A Quincy-Stamped Universal Joint That Never Took a Shift
Condition
Unused new old stock. The hubs show fine handling scratches across the barrel where the name is stamped, and the set screws show bright metal in and around their sockets where a driver has seated them. The dark finish is even across both hubs, the yoke ears, and the center block, but one bore rim carries a brown granular crust along its edge and the set screw counterbore in the end-on photo shows a bright, torn lip, so judge those two spots off the photographs rather than off any blanket clean bill from us. One of the two shaft keys is missing; a key is seated in the keyway of the bore shown end-on in the photos. This joint has not been run under load, checked for angular play, or gauged for bore tolerance here, so the photographs and the stampings are the specification for the piece you are buying.
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Product Overview
This is a single Boston Gear J125 universal joint, the block-and-pin type you can see plainly in the photos: two bored hubs, two yokes, and a center block carried on cross pins whose ends sit flush in the yoke ears. Both hubs take a 3/4 inch shaft, each is broached with a keyway, and each is drilled and tapped for a set screw; in the end-on photo that set screw sits well to one side of the keyway rather than over it, so do not count on the two lining up. One hub also shows a small second hole alongside its set screw that these photos do not identify. Overall length is 3-3/4 inches, and laid against the millimeter scale the joint reads roughly 108 mm end to end with the hubs about 33 mm across, but the body stands well proud of the ruler plane and that parallax runs the scale long against the 3-3/4 inch figure, so treat both reads as approximate. The original listing data gives a maximum connection angle of 30 degrees. The body is stamped BOSTON Gear with the registered mark, J125, and MADE BY BOSTON GEAR WORKS, QUINCY, MASS., U.S.A., the lines running around the plain round barrel of the hub and curving with it. Construction is steel; the specific alloy and heat treatment are not confirmed here, so verify against the Boston Gear datasheet before use. One shaft key is included and the second is missing, which the closing questions below spell out.
Key Features
- 3/4 inch bore at both ends, each keyed and each fitted with a set screw offset to one side of the keyway
- Overall length 3-3/4 inches; reads roughly 108 mm against the millimeter scale, run long by the part standing proud of the ruler
- Block-and-pin single universal joint, hubs approximately 33 mm across at the scale
- Maximum connection angle of 30 degrees per the original listing data
- Stamped BOSTON Gear, J125, MADE BY BOSTON GEAR WORKS, QUINCY, MASS., U.S.A.
- Steel construction; alloy and heat treat not confirmed - verify against the datasheet before use
- Dark, even finish across the hubs, yokes, and center block, with a brown granular crust on one bore rim and a bright torn lip at one set screw counterbore
- Unused new old stock, sold as the single joint pictured, with one of its two shaft keys
Applications
- A maintenance tech pulling a seized joint out of a 3/4 inch jackshaft drive and wanting to put the original Boston Gear number back in rather than gamble on a cross reference.
- A machine builder tying a 3/4 inch drive shaft to a hand crank, encoder, or gearhead that sits a few degrees off the driving axis, comfortably inside the 30 degree rating.
- A shop restoring an older machine tool or line shaft setup who would rather fit a joint carrying the Quincy stamping than a modern import of unknown parentage.
- A test rig or prototype build needing a short, keyed coupling between two 3/4 inch shafts that will never quite agree on center.
Frequently Asked Questions
What shaft size does this joint take?
Both ends are listed at 3/4 inch bore, keyed, with a set screw at each hub. Bore tolerance and key stock size are not confirmed here, so measure your shaft and check the Boston Gear datasheet before you commit to it.
Does it come with both shaft keys?
No. One key is included and you can see it seated in the keyway in the end-on photo. The second key is missing, so plan on cutting or buying a standard key for the other hub.
How far out of line can the shafts run?
The original listing data gives a maximum connection angle of 30 degrees. Angle costs you velocity uniformity and bearing life on a single joint, so keep the working angle as small as your layout allows, and confirm the rating against the Boston Gear catalog for your duty cycle.
What exactly is stamped on it?
BOSTON Gear with the registered mark, J125 below it, and MADE BY BOSTON GEAR WORKS, QUINCY, MASS., U.S.A. under that. The photos show the stamping close enough to read, which is the point of shooting it that way.
What am I actually taking on with a surplus joint like this?
Exactly what the photos show and nothing hiding behind them. It is unused new old stock, it carries one of its two shaft keys, and it has not been turned under load, dial indicated, or bore gauged on our bench, so the stampings and the pictures are the whole specification. You are buying the specific piece we photographed, markings and missing key and all, instead of a mystery joint out of a bin. This item clears our free shipping threshold on its own, and orders leave the Idaho warehouse the same or next business day.
The Quincy stamping is still crisp on a joint that never had to explain itself out on a running shaft. Hand it two 3/4 inch shafts that refuse to agree on an axis, and it finally gets to do the one thing it was machined for.
