Use of Self drilling screws-

I am trying to use S-MD 12-24 for 2 metals having overall thickness 1) 0.5" and 2) 0.8".

For 1) - S-MD 12-24x1 1/4 HWH #5 says Max dril capacity as 0.5" but MT as 7/16" (less than 0.5") Can you clarify why the discrepancy (What's diff between MT and Max Drill Capacity) and if there would be any reduction in shear capacity than what's shown on tables.

For 2) - Can I use S-MD 12-24x2 HWH #5. If not what product can i use. There is 1/4" bolt but dint find shear capacities in the table.