Question: so I accidentally screwed the wrong side pedal into my left hand crankarm on my [Giant Defy 3 2014](http://www.giant-bicycles.com/en-au/bikes/model/defy.3/14893/66357/), and I have been looking to buy a replacement part myself and get a mechanic to install it. 

I am wondering what would be compatible with the original Sora groupset components? I haven't been able to find just a crankarm, so I am looking to buy a crankset.

I can get a [Shimano Sora Double 3550 9 Speed Chainset](http://www.ribblecycles.co.uk/sp/road-track-bike/shimano-shimano-chainsets-road-shimano-sora-double-3550-9-speed-chainset/shimchar491) for 40GBP. 

Would other 9 speed cranksets work?

What other left hand crankarms would be compatible?

Thanks.

Answer: 
If you're replacing the whole crankset and BB, then any 9-speed double crankset should work. The chain width for 9-speed systems is the same for all makes (not the case for 10 or 11 speed).

But before you do that, I'd look around and see if you can replace just the left arm. Any crank designed for the Shimano "outboard bearing" BB should work (those are the ones that clamp onto the BB spindle with two pinch bolts). Just make sure the crank arm is the same length.
You may well get a bargain like @Klaster\_1 mentions in your comments.

If you did want to buy a new crank set that behaves exactly the same, you could get anything that matches the same specifications: 

1. [Bolt Circle Diameter](http://www.wolftoothcycling.com/pages/how-to-measure-bolt-circle-diameter-bcd),
2. the teeth count (in your case 34/50 if you're replacing that sora one)
3. ensure that its got the right shape hole for the bottom bracket spindle (rarely incorrect)
4. crank arm length

If you have a Sora groupset already then you may get a smoother experience from getting the same model crankset, but this is down to opinion, and I haven't had any issues with mixing.

As usual, your local bike shop will be able to give you plenty of information.