There’s a small fine-thread adjusting screw on the end of a plate level on my transit, and I wonder what the name of this screw head is and whether there is a nice wrench made for it.
The screw head is a cylinder 7.5 mm in diameter and about 4 or 5 mm tall. There are six blind holes arranged radially around its OD. The holes are 1.5 mm ID or within several mils of that. They only look a couple mm deep. If you put six pins in these holes, it’d be a six-spoked wheel without the rim.
The instrument maker describes a “pin wrench” that has a cylinder fitting into any one of the holes, but I haven’t been able to buy one of these. I have used the shank end of a drill that seems to be about 3 mils shy of the right size, and this works but it is flexible enough that I don’t get as close as I would like. I think I could get the screw within about half a degree of the right position if the wrench were stiffer.
I can buy precision solid steel pins of 1.5 mm diameter, which would be a bit stiffer than the drill shank.
But I can picture a wrench that would put pins into opposite faces of this screw and would be much stiffer. It’d only have to be the size of a finger. I’d like to find such a thing. Even a bar 5 by 10 mm by 50 mm long, with intersecting 1.7 and 1.5 mm holes drilled near one end, would be perfect to use with two free pins.
Anybody know of such a wrench?
Anybody know what this style of screw head is called?
I have seen a tool for this, though it was made for a larger diameter cylinder. It looked like a question mark, and it had a short pin protruding from the free end of the arc. Speaking of drills, though, have you tried snugging a drill chuck on the screw head?
I think you’ll find the indicated wrench is of this type. There’s also one pictured near the bottom of this page. Note that only one hole needs to be engaged, the curvature of the wrench applies reactive force to the side of the screw head.
You might be able to find the right size at a specialty tool store, or you might be able to fabricate one like those pictured. The shortness of the pin pretty well eliminates any concerns of stiffness - you could use your drill bit (broken off) for the pin.
It is a similar tool, specifically a “hook wrench.” For the screw head described in the OP, though, with round holes rather than squarish slots, a pin wrench would be needed. The real challenge is the size - bottom bracket nuts are 40+ mm diameter, while this screw is <8 mm diameter. Finding one that small may be tricky.
If you or a friend have a drill press and a hacksaw, you can make one easily by drilling a hole in the face of an 8mm spanner in which you would press fit a pin ( or broken bit of one of the drill bits) , then cut out about 1/4 of the wrench diameter with the opening produced just a few mm from the pin.
Yes, I have seen hook wrenches, though I didn’t think of them. I don’t know if it would work, because this is an adjustment screw and you want to be able to fine tune it back and forth. The hook wrench turns the screw clockwise if you hold it like a question mark. To turn counterclockwise, you have to take it off, flip it over, and hold it like a sloppy unclosed number “9”.
It wouldn’t be hard to make. I have a drill press and vise and little bits of brass, and a 1.5 mm drill is certainly cheap.
>snugging a drill chuck on the screw head
Good idea, but there’s little room next to and above the head.
I have seen many wrenches and pliers comprising two pins that are parallel to one another and stick into holes in the face of a screw or nut. They are often used in optics, for example. Here, we just want to turn them inward toward each other. I just know there’s a name for this and a wrench for this out somewhere!
One last thing, a dumb error - I remembered wrong, it’s the nut I’m talking about, not the screw head. But I think that doesn’t change anything.
If this wrench doesn’t need to apply much torque, you might be able to use a pair of snap-ring pliers (the kind with removable pins, like this one; use the bent pins and turn them inward).
