I built a fairly utilitarian work bench last year on 3 inch casters with one bottom shelf.

I used 3 inch wood screws, 2 on each face of a joint. Thing is a tank with 4x4 legs and 2x4s everywhere else.

Plenty to hold a table saw, mitre saw and anything else I regularly put there.

Only place I used lags was to secure the casters to the bottom.