As 1 2 trowel means that both measurements are the same.
Trowel for wall tile.
1 4 x 3 8 square notch.
Tile trowels come in many shapes and sizes generally starting out from a 3 16 v notch up to the 1 2 square notch finding the right trowel for the job is quite simple when you know that generally speaking the trowel size should match up to the tile size the smaller the tile the smaller the trowel.
A tile trowel with only one measurement i e.
Use this for 8 8 s and some of the 5 16 thick 12 12 builder grade tile.
The larger the tile the larger the trowel.
Anytime you use 12 x 12 or smaller vertical wall tile you always use a v notched trowel rated for tile installations since it is made specifically for vertical surfaces to bond the mastic mortar successfully.
Mosaic tiles and wall tiles up to about 4 by 4 inches call for a v notch trowel with 3 16 by 1 4 inch notches while larger tiles require a trowel with a square or u shaped notch to obtain proper adhesive coverage.
This may also be a good trowel size for thicker 5 16 mosaics.
Twelve inch square tiles for instance are best applied using a trowel with 1 2 inch by 1 2 inch notches.
Also make sure the thin set mortar you hand mix yourself is also rated for vertical surfaces.