18350 = 18mm diameter battery
16340 = 16mm diameter battery
The first two numbers are the diameter in mm.
The second two numbers are the length in mm.
The 5th number is form factor, 0 is cylindrical.
Mac's Tri & EDC 2.8 amp should both use imr cells (as it's a high drain application).
If you use use a 16340 in Mac's Tri you should be using a 16340 imr.