The ER-16 and ER-32 collet chucks use an M12×1.75 bolt to snug their MT3 tapers in the Mini-Lathe spindle. As nearly as I could figure, I needed a 190 mm bolt to get enough thread engagement, but the nearest available sizes were either too short or too long.
Fortunately, making round things is what a lathe is all about:
The aluminum bellyband adds 30 mm to the length and aligns the bolt sections, with the threaded section from a long 5/16-18 bolt inside holding the metric bolt together:
Although I got it right on the first try (!), the bellyband lets me fine-tune the length as needed.
The original dimension doodle and some in-flight updates:
The fancy brass / bronze washer comes from a battered rod with mushroomed ends. A pair of V-blocks let me cut a chunk off one end with negligible drama:
It’s clamped firmly to the right block and a few licks with a file knocked off enough of the mushroom on the left end to put it flat(-ish) into the V; the near side of the right block is barely raised off the surface.
Face off the mushroom to get a flat spot for a center drill:
Some peaceful turning & boring produces a pretty washer:
The bore needed a bit of relief to seat the bolt head squarely on the outer surface:
And then It Just Fit™:
Loctite on the inner bolt threads should keep everything together.