2u, 2.25u
and 2.75u keys all have the same stabiliser. The stems are 1.25u apart (centre of mount to centre of mount).
On standard space bars, each stabiliser stem is 0.5u from the edge (left or right). In other words, a 1×1 key could fit on each stem right next to an Alt key.
Standard space bars have the switch in the exact middle. Some Cherry-brand keyboards (G80-series, 6.25u or 6u) have the switch somewhat offset though, and some DIY keyboard PCBs and plates are made to fit these dimensions too so that vintage keycaps from those keyboards can be used. Some vintage keyboards have space bars 8u or longer: these all use stabilisers for 8u.
https://deskthority.net/wiki/Space_bar_dimensionsI use QCad to draw plates. It is free to use and uses the DXF file format.
It allows me to create a template "block" for each key with the outline in one layer and the plate cutout in another. Then I enable snapping corner to corner (line "end") when I lay them out.
I also have a layer for "guide lines" to draw lines for aligning things and to make lines with specified lengths from dimensions in switch manufacturers' drawings. To find the centre of a rectangle, I draw guide-lines between opposite corners and snap to the intersection point.
But... The plate builder is much easier to use if you're making a traditional keyboard.
BTW:
* Be aware that the Costar stabiliser mount's rectangular hole is not centred on the mount's. It is somewhat offset in height, and the direction is significant: the wire must be on the same side as the switch's LED.
* You may also find a combined cutout shape that fits both Costar and Cherry plate-mounted stabilisers.
* Switch cutouts that have small notches are for allowing opening of switches in place without desoldering. Those work with Cherry MX and direct clones but not with Kailh (and some others) that have a single large snap on each side instead of two per side. I think the combined Alps/Cherry hole shape could work with Kailh switches though.
