Check here https://www.husqvarna.com/us/lawn-and-garden/buying-guides/bar-and-chain-fit-up-chart/
Looks like it should be .325 pitch and .050 gauge. It should also say on your bar as well. Check this before you buy.
To answer your question for Amazon link, this is a 20” .325 .050 chain. Says it will fit a 450. Again make sure the drive links match what it says on your bar.