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SX230HS Adapter: Mounting Screws
The microscope adapter needs a single screw to hold the camera to the mount. I used the same aluminum knob as on the adapter for my previous camera, shortening the screw so it didn’t bottom out in the camera socket:

Shortened camera mount knob screw The boss is slightly shorter than the recess, so the knob body seats on the plate and works like this:

SX230HS microscope adapter – side view When the camera isn’t on the adapter, the screw stores neatly in the 1/4-20 nut sunk in the middle of the mounting plate.
Although I can hand-hold the macro lens adapter, it’s much more stable on a real tripod. That requires a flat camera-mount screw that sits within the recess so the mounting plate can sit flush atop the tripod head:

Camera mount plate with screw – bottom view However, it’ll be much easier to use the knob screw when I’m hand-holding the thing, so I drilled-and-tapped a hole in the knob for a place to store the flat screw when it’s not in use:

Camera mounting screws – end view The threads in the knob don’t go quite far enough to seat the screw head against the knob, but that crude hack wouldn’t work in aluminum. Fortunately, it doesn’t matter:

Camera mounting screws – joined This being a low-torque application, I filed the top off the already-pretty-flat truss head so the mounting plate recess didn’t have to be all that deep.
The knob+screw stores in the 1/4-20 nut between uses, too:

Knob and screw stored in macro adapter Yeah, yellow probably isn’t appropriate for an optical structure; I’ll shoot a black rattle-can coat inside there after the weather warms up…