Ultegra Crank Arms
 

Can the Ultegra crank arms between a double and triple chainring be interchanged? I want to swap the crank arms from my Ultegra triple to my Ultegra double (and visa-versa) and was wondering if it will work?

isnt the drive side different the double doesnt have mounts for a 3rd sprocket and the bb's are different. if you are switching the entire unit bb and all you should be good.

I just want to change the crank arms and nothing else. I want to remove the crank arms from both chain rings and just swap the crank arms and not the whole crankset. Essentially, I want to go from a triple to a double with a shorter crank arm, without having to buy a whole new crankset. If it was double to double or triple to triple, I know I can do it. But since it's going from triple to double and visa-versa, I want to make sure I can do this before I start taking the crankset apart.

Yes, the middle and big ring on your triple will fit a double. But ultegra doubles use 39/53 rings and you will end up with 42/52. The ultegra double uses a 109.5mm BB and the triple uses a 118.5mm BB.

Can I just move the crank arms and not any rings?

The BB in your frame has a 118.5 spindle for a triple crankset. a double uses a 109.5 Bb spindle length.You can stick the double crankset on the triple spindle,and the sun will still come up in the east, but the chainline will be less than optimum.

If you are planning to use the triple crankarms with the double's chainrings, no problem. The other way around (double crankarms) you can install the two larger chainrings of the triple set but won't have any threads for the small ring.
Your double probably came with a 53-39 combo while the triple came with a 52-42-30. The triple crankset may become a 53-39-30, 52-39-30, or a 53-42-30. The double crankset may become a 53-42, a 52-39 or a 52-42.
I use a 53-42-30 combo on my triple.

Cool! Thanks for the replies. :)