I have a .223 Wylde SS barrel that has a 5/8-24 thread. I am having trouble finding a muzzle brake / compensator that matches the thread size / caliber. I understand that a non threaded would be more accurate but I wanted the ability to add a suppressor later. If I just use a threaded cap and a crush washer, can that throw the accuracy off? If so, any suggestions on a brand. All daytime shooting, so not too worried about flash.
Any advice would be appreciated.

Well if your positive its a 5/8-24 thread as most 5.56/.223 are 1/2-28, then what you seek is a 7.62/30 cal. muzzle device and there are plenty on the market.

That's weird, a .223 Wylde barrel with 5/8x24 thread size (7.62 cal).

 

What brand/manufacturer was that barrel?

AR Performance has a couple of brakes for .223 with a 5/8-24 thread if you are sure that is what you have.
http://ar15performance.com/muzzle_devices

You can probably get a Ross Schuler brake made for .223 with that thread pattern.

It is a Wilson Combat SS 18" Super Sniper