I have updated the lower mount.
It now has a pin that fits the heat bed.
I used peaberry's hotbed mounts, but made these glass mounts.
Peaberry's bed mounts: http://www.thingiverse.com/thing:1982435
Because I'm running a BLTouch that hangs out a little, I wanted the holders for the glass on my hotbed to be as low as possible to avoid any chance of contact with the BL.
These fit below the hotbed, that is, not supporting it, gap around the hotbed and are flush with the top of the 3mm glass surface (except for the head of the bolt).
I printed both his mounts and these mounts in PLA to at least get me printing with heat, but if they show signs of softening with higher temps, I'll redo them the ABS or PETG.
You'll need to print 3 X of both parts.
The lower part mounts to the beams with 2 X 3mm bolts and T nuts. And the upper part is bolted using a 3mm bolt and nut.
You may need support for the nut cavity, is so, be sure to get it all out prior to inserting the nut. It's a blind hole, so only one way in and out.
Because of the tension towards the glass and the compression from the hold down bolt, I went heavy on everything. I used 4 bottoms, 4 tops and 6 perimeters @ .2 and 60% infill.
IMPORTANT! These mounts DO NOT clamp the glass down in any fashion. They only apply pressure to the edge of the glass. It's enough to hold the glass in place and keep it from moving or spinning during printing, but if you turn the machine up-side down, the glass may fall out. Also, since they don't clamp, be sure that your heat bed is actually as flat as possible, without any type of convex to it.
Because of the blind nut cavity you may need to use a little bit of support. Be sure to get it all out of the cavity before trying to push the nut in. Mine went in tight, with a little help from small hammer.
Don't overshoot the hole with the nut.