Do these blades fit a Sears Craftsman model 320.61199

This is universal so will fit most major brands tools.

Yes, they should fit your Craftsman Nextec Multi-Tool. These accessories have a universal arbor, and reviewers have commented that they fit Craftsman cordless and Fein oscillating tools in addition to most other brands. I also own this set, and I assure you with great confidence that you will not find a better value than these Blue Hawk accessory kits. You may also wish to consider the Blue Hawk 24-Piece Oscillating Tool Accessory Kit (Item # 506139 - Model # BTA30204) which recently came back into stock after a short absence at Lowe's. That set has some additional tools not included in the 18-piece set and is available at most Lowe's store locations and on the Lowe's website.

The only way to know for sure is to buy it and try it. If it does not work you can return it. I bought it for and use it with my Rockwell Tool