I use some Dial Test Indicator (DTI) magnetic stands purchased at low cost on Aliexpress. There are two types.
Above is the small type with a rather simple clamp for the DTI.
Above is the larger type which has an DTI clamp that allows small adjustment of the dial reading (the adjusting knob is hidden here.)
The problem
Both of these have an annoying problem in that when the handwheel is moderately tight but still allowing adjustment of the arms, the handwheel follows the left hand arm and so tends to tighten or loosen as the other arm is rotated. One of those problems that would be solved by having a third hand.
So, an improvement occurred to me. The problem is that the friction from the handwheel to adjacent arm’s centre cam / boss is higher than from handwheel to threaded shaft. What if a thrust bearing was inserted between handwheel and the cam / boss?
Above, a F5-12M 5x12x4mm thrust bearing, <$10 per 10 on Aliexpress.
Above, the outer cam part in a 12mm collet chuck ready to take 4mm off the length.
Above is a close up of the thrust bearing fitted to the larger stand. There is little clearance for foreign matter to enter the bearing, but it is easily cleaned and oiled if the handwheel is loosened a couple of turns.
Does it work?
Yes, at the tension typically used when adjusting the stand, the handwheel stays with the threaded shaft, tension remaining consistent… so a third hand is not needed to readjust tension whilst adjusting the arms. Of course the handwheel needs to be tightened further when the setup is final.
Of course with the reduced friction using the thrust bearing, lower torque is required on the knob to achieve the same ‘locking’ friction in the stand joints.
You may have observed that these stands appear to be ‘inspired’ by the Italian Noga stands which sell here for more than 10 times the price of the Chinese jobbies above. Noga may use a ‘proper’ thrust bearing in their product, I do not know.
Experimental
Above is an experimental configuration using an M5 clamping lever and a short piece of 13/15mm silicone tube to protect the bearing from debris.