United Scientific™ FG4980-3000, 3000mL (3L) Borosilicate Glass Erlenmeyer Flask (Single)

I bought this to make yeast starters for homebrewing. Unfortunately, the bottom is concave enough that it won’t work. I’ve tried it on two spin plates with no success. The stir bar inside the flask can’t get enough of a magnetic connection with either plate. Bummer since this appears to be pretty well made and the measurement lines are pretty accurate. Would return but I’ve already tossed the box it came in.