TG stands for “three guides” What’s special about this is the number of guides are reduced from 4 to 3 and that works to prevent missloading of very small IC packages.
Small IC packages such as 2×2 can also be accommodated onto IC trays with this patented design.
Due to being symmetric, the 180 deg rotated trays also stack each other.
It is not symmetric, the 180 deg rotated trays cannot stack each other.
In the limited space, if top guides are designed to be bigger to minimize rotations of IC packages, engaging counterparts on the back side guide lengths are limited which will cause dislodging of IC packages.
In the limited space if top corner angles are designed to be deeper & bigger to absorb rotations of IC packages, automatically (due to tray height being limited) engaging counterparts of the back side guides will be shallower which may lead to easy dislodging of IC packages.
TG design can achieve both rotation & dislodging preventions at the same time.