What information do I need to check before buying linear rails for 2020 aluminium extrusion?

My alternative linear rail device turned out questionable after two weeks of spending and cost of $40 dollars.

I designed a L bracket that serves as the carriage and linear block that moves along 2020 aluminium extrusion, ordered three parts from a manufacturer.
The quality wasn't up to my expectation, 0.1 mm of thickness difference.


Anyway I let the machine shop make four threaded holes and got them after one week.
I mounted the L bracket directly on the 2020 aluminium extrusion with two pairs of T bolt and T nut slides up and down along the extrusion. The friction between the L bracket and the extrusion often developed biting force that stops movement of the bracket.

HIWIN MGN-12H


According to the datasheet of MGN-12H, the height of carriage is 13 mm. I think if I buy a linear rail that's not 13 mm, I need to adjust the position of motor pulley and bearing position of the top vertex frame. Am I understanding it correctly?

Thanks in advance,
Hughe