Thread: T-knobs, what are they for?

Do they have a hex recess on the mounting face side that would accept the head of a bolt or hex screw so you could attach it to form a tweeker of your prefered size/length? Agreed that there is very info in the web description of the item.

A fine mystery.

The page one level up says this:
1/4" & 5/16" Thread Diameter Jig & Fixture Parts

When making jigs and fixtures, it's always a chore to find hardware of the correct size. This well-coordinated line offers a solution. We have parts with 1/4" (6.35mm) - 20 threads for general use or with more robust 5/16" (7.9mm) - 18 threads for increased durability. The components can be intermixed as long as they share a common thread size; the knobs and handles can be combined with the nuts, inserts or machine bolts.

Made from durable plastics, the taper handle and the ball, clamping, sure-grip, 1-1⁄2" four-arm, wing and bar knobs come in both male and female configurations; all have a 1" stud unless otherwise indicated (see product descriptions for more information). The 2" four-arm and pentagon knobs are female only. For a custom thumbscrew, press-fit (vise assisted) the socket head of the capscrew into one of the three available knobs; rose, knurled or T-knob. Use the appropriate nylon washers as spacers or when you have to apply pressure right at the capscrew head. The jig handle, wing nuts and thumbscrews (threaded shaft length listed in chart) are made from malleable iron for extended service.

Please note in our descriptions that '(F)' denotes female thread and '(M)' denotes male thread.

In particular: For a custom thumbscrew, press-fit (vise assisted) the socket head of the capscrew into one of the three available knobs; rose, knurled or T-knob.

Which leaves us with the next mystery: What's "the socket head of the capscrew"?

Parts like that usually have a threaded metal insert embedded during molding. Yours might have escaped the embedment process, and could be duds. I suggest you contact Carbatec with your concerns.

"Socket head of the capscrew" refers to a hex socket bolt with round knurled barrel head, like the one on the right here: Hex Socket Screws, Socket Head Cap Screws

Cheers,
Joe

Emailed Carbatec, and received a phone call in reply, advising that these little knobs were supposed to be a press fit over the bolt head, and that there was no thread in the smaller ones I cannot see any use for them.

They did offer to credit me the amount if I returned them, so they are in the mail.

Sounds like these are designed to be pressed over an Allen headed bolt but I'd want them with a hex recess so they can be pressed onto a normal hex headed bolt; you'd get better torque.

It's good that they're crediting you back the purchase price.....it'd be fantastic if they refunded the postage too!