More than likely, he currently has a nutted axle. A lot of cheaper bikes have 3/8" (9.5mm) nutted axles. Swapping an axle out on one of these bikes would require new cones as well because the 3/8" threaded cones will not fit a 9mm axle. It can be done, though, with the right parts. An option for the conversion is available here: Wheel Master Threaded Quick Release Axle - FT, 9 x 1 x 100 x 108

Note that you'll need a front quick release skewer to complete the conversion.