Perhaps it would be helpful if you said why you needed 3 7/8" squares. I'm sure there are many members here that could give tips on how to avoid those awkward sizes. If you are making half square triangles it is much easier to go up to the nearest whole number, in this case 4", and then trim your HST down to size. You get much more accurate HST that way.
If you are making something else where you need 3 7/8" squares I'd be interested in hearing others tips on this.