I was able to -force- TPR-1k's into a breadboard without breaking anything, but it wasn't real easy.
I was using them to adjust leds with 5Vcc. And... I actually only got 5 per $1. :-(http://www.allelectronics.com/make-a-store/item/TPR-1K/1K-VERTICAL-ADJUST-TRIMMER/1.html
Some others, no, they would need wire leads soldered on. None of them I know can't take 5V 40 mA.
When you see leads on 5mm centers, 1mm is very close to .04" where breadboard holes are .1" apart.
I had more trouble with he width of the legs but even without squeezing the legs in a crimp tool, they fit.
They have some with pins on .1" spacing but more expensive and the ones 10/$1 don't all just fit.http://www.allelectronics.com/make-a-store/category/470100/Potentiometers/Trimmer/1.html
How much they can take, I don't know but I can say; more than a poor little IR led!
Consider 5V 20mA is .1W
If you call and ask they do have an 888 number and I have gotten info when making phone order long ago.