Knape & Vogt Vogt 0202-10Pm Heavy Duty Shelf Standard, Platinum, 10-Inch

what is the slot width?

Can I adjust Mount these below my flat screen and put my soundbar on it?

Are these able to be cut? I don’t need 45 inches, more like 12.

I have commercial shelf 4ft long x 22 inch deep. W/ 3 notches to hang the shelf each notch has a 1/4 inch opening. Do you think this works?