Thank you for your question about Master Caster Deluxe Casters.
Master Caster makes stemless casters specifically designed for chairs with welded stems. However, almost all chairs of that type have stems that are 3/8" diameter. Before you buy, please re-measure your stems. Stemless casters can only be applied to 3/8" diameter stems.
If you re-measure and find that your stems are indeed 5/16" diameter, I am 99.9% sure they can be removed. Of course, that is sometimes easier said than done! If you are having trouble removing your chair stems, try using the claw side of a hammer to work them out of the base. A little WD-40 wouldn't hurt at this point either.
No matter what type of stem you use, make sure you get the right type of wheel for your flooring. Hard wheel casters for carpeted floors, soft wheel for hard floors and chair mats.
Hope this helps!