Does magnet shape matter?

[Piston_Pounder]

I got a 40mm by 15mm neodymium or however you say it, rare earth metal magnet to paste on the top of my fan. Long little rectangle. It's about 1/8" below the stir bar and Ive started slow and yadda yadda but I can't get it to grab the bar!

Is this a reason everyone uses the crescent shaped magnets out of a hard drive?

 

[JBOGAN]

Just recently went from one to two stir plates and purchased magnets the same as you have from K&J . Here is my configuration.

 

[JBOGAN]

I found out that less is more.

 

[Sellick]

I found that for the 40mm stir bar it helps to have two separate magnetic points on the washer for the stir bar to connect to. Immediately solved my magnet problems. Just have to make sure your magnets are flipped the correct way to grab the two opposite ends of the stir bar!

EDIT: realizing now that 40mm is the length of your magnet, not your stir bar. What's the size of your stir bar?