This is a T-Nut with a 3mm nut imbedded in it for use with openbuilds rails.

Geeetech Pro

No

No

.2mm

100%

Nuts just fit. might need a drop of crazy glue to hold them in or shrink the size down a bit.

Needs a little cleanup on the 3.5mm hole for the bolt if you squish your first layer down too much!