What size stir bar in a 1000 ml flask?

[ontap@home]

I have about a 1 1/4" bar now. As I turn up the speed, it get slung out of the center. Any advice?

 

[Brewer3401]

Try using smaller stir bars. The smaller they are, the faster you can spin them.
Small ones are good if you need shearing, and bigger ones are good for high flow.

 

[rdwj]

Funny, I always had trouble with the smaller ones. The bigger ones never seem to spin off center for me. Then again, I have a 2000 ml flask

 

[Brew-boy]

I use a 1" stir bar in my 1000ml, works great but it does have a center ridge on it.

 

[Yuri_Rage]

Flask size isn't really the problem here...it's magnet strength and the distance between them that matters. The closer the stir plate's magnets are together, the smaller the stir bar you can spin. The stronger the magnets are (or the closer you can get them to the stir bar), the larger the stir bar. There's a happy medium somewhere...

I can successfully spin everything from a 1/2" to a 2" stir bar in a full 2L flask with two 5/8" diameter rare earth disk magnets spaced roughly 1.5" apart on top of a computer cooling fan.