Hoop,
I also think that with the XHP70 and MT-G2 leds, you might need to see what you can come up with that would center them on 20mm stars and 26mm stars. I think that most of us have to open up the reflectors to fit, so having pre-made washers where you tell us what the ring OD would be might be good. We would then just be able to open the reflector hole to fit.
One big issue is that the XHP70 stars are only 20mm and with the diameter of the led base, there is not much room at all for a ring, since it's already very close to the solder pads. The same is true with a 20mm MT-G2 star.
Here's some specs and thoughts:
XHP 70 led - The center square cut out would need to be 0.275" and with a 20mm Sinkpad, the best way might be to make the spacer rectangular at 0.350" wide and 0.675" long. That will fit within the solder pads. The thickness of the led base is 0.037", so a 0.040" thick spacer would bring the reflector just a couple thousands from touching the led base.
The MT-G2 led - The center square cut out would need to be 0.365" and with a 20mm Noctigon a rectangular spacer would again be best, with a 0.500" width and a 0.700" length. The thickness of the led base is 0.035" so again, I would go with a 0.040" thickness.
On a 26mm Maxtoch star, there's lots of room for the MT-G2, so a spacer could be made at 0.800" OD and the center square at 0.365".
Those are just flat spacers. From the dimensions, you can see it would be hard to make actual centering rings for them. If you were to make them with rings, then here's some ring dimensions:
XHP 70 - 0.388" ID and 0.420" OD
MT-G2 - 0.498" ID and 0.510" OD
That gives a ring thickness of 0.020" As far as ring height, I would go with something like 0.100" tall and people could sand them down if they wished.
In summary:
XHP 70 on 20mm Sinkpad - A rectangular spacer measuring 0.350" wide and 0.675" long, with a 0.275" center square hole and a ring that was 0.388" ID and 0.420" OD. Of course that own't work, so the ring would have to be made where it was formed only on the long sides that had room for it.
MT-G2 on 20mm Noctigon - A rectangular spacer measuring 0.500" wide and 0.700" long, with a center square hole of 0.365" and a ring that is 0.498" ID ans 0.510" OD. Again, that means the ring would have to be made where it was formed only on the long sides that had room for it.
MT-G2 on 26mm Maxtoch star - A round spacer with an OD of 0.800" and a center square of 0.365", with a ring of 0.498" ID and 0.510" OD.
I would suggest the thickness of all the spacers at 0.040". The reason being that most, or many of our reflectors have flat bases with no space for wires and the 0.040" will at least let 22 ga teflon coated (teflon gives a very thin coating, where silicon its too thick), wires crushed flat, to be soldered on and still clear the 0.040" thick spacer between the reflector and the star.
We would simply drill or bore out the led holes of our reflectors to fit the rings. That might be best, since most of the reflectors are not made for the MT-G2 or the XHP-70.
OK, I'm done.