What are these square-lobed 4- and 6-sided screw heads used in the Reichert 410 Microstar IV?

[hans]

The small, 4-sided set screw heads were mentioned in posts #2 and #7 discussing Brian's camera adapter. On both of them the recess is straight with the same profile all the way to the bottom. On the larger 6-sided ones a Torx T9 bit works ok, but has to be forced in the first time (outer diameter slightly too large) and there is some rotational play since the Torx points are narrower than the slots in the screw head.

[MichaelG.]

I think they are [or at least, were] Bristol Spline

Regrettably scarce this side of the pond, but you should be OK
https://www.mcmaster.com/bristol-splines/

MichaelG.

[hans]

Thanks Michael, looks promising, I measured and they match closely the available major diameters 0.048" and 0.096", going to add those sizes to my next order.

...[or at least, were] Bristol Spline

Ha, yeah, not sure I have any that are unmolested by Philips/Torx/hex bits. As I mentioned in the other thread I actually already replaced all the smaller set screws with normal hex socket ones out of frustration. And by now the larger ones (which hold the binocular and trinocular heads together) are all, lets call them, T9-modified 0.096" Bristol splines.

[apochronaut]

Bristol spline drives, as well as a number of other heads with unusual sizes or formats get used in optical designs for two reasons. One is that certain drives are more secure when used in applications where the dimension is small or the material softer. The other is to avoid tampering, the intent being to dissaude users from attempting to adjust or disassemble components which are critical to functionality and might be difficult to reassemble or readjust. Kind of a way to steer owners towards using their service techs.

[hans]

...the intent being to dissaude users from attempting to adjust or disassemble components which are critical to functionality and might be difficult to reassemble or readjust.

Indeed, this brings up something I have been wondering about for a while:
How to set tube length on the fixed (without diopter adjustment) side of the Reichert 410 Microstar IV binocular head?

[hans]

Thanks Michael, looks promising, I measured and they match closely the available major diameters 0.048" and 0.096", going to add those sizes to my next order.

...[or at least, were] Bristol Spline

Finally ordered them and they fit perfectly, thanks Michael. McMaster-Carr part numbers 7048A12 and 7048A18 are the exact ones I got.

[BadDog]

Hi,

Are these the same sizes used in the AO10? (McMaster-Carr part numbers 7048A12 and 7048A18)

Thanks!

[apochronaut]

Those are larger. The screws on the series 10 head are 6 flute .048". I don't know the McMaster-Carr number. Newman tools not too far from me near Ottawa has short and long Bristol keys. They used to have a facility in Harford Ct. too but it doesn't seem to have an address or phone as of just after Covid. Newman has a toll free. Perhaps they still ship out of Harford but the Ontario plant handles all of the orders.

[hans]

The tiny set screws that fix tube length on the nonadjustable eye tube on are the same 4-flute 0.048" McMaster 7048A12. The four screws holding the shroud covering the IPD adjustment are 6-flute 0.060" McMaster 7048A65. I don't remember if there are any others on the series 10 heads. I also have a 6-flute 0.072" but don't remember what it fits, possibly I ordered it by mistake.

[apochronaut]

Good thing you caught that, Hans. I think it a key for the "I" shaped cover plate cap screws required. .060" is the size.