lamp bracket undermount

The clamp for my swing-arm lamp broke. I found this thing and made it:
https://www.thingiverse.com/thing:21479

but it's only the top. so i made the bottom myself. This one is much beefier than the original. Designed in blender.

Mine was printed out of black ABS. i had some warping on the bottom, so i sanded it flat with 80 grit sandpaper after. I did an acetone vapour bath after to clean up the lines. Both pieces actually got the same treatment (top and bottom). I still had the metal bolt, the nut, and the plastic knob from the original lamp base.

I originally created this piece with the hole sized 8mm, which is what i measured the bolt to be, but then i found the threads were a bit bigger, so i had to drill it out. I've increased the hole size to 9mm in the design so anyone else printing it won't have to do that.