1/2x28 is typically reserved for .223 caliber and smaller, although there are exceptions to this; Fierce Firearms, Edge model for example in 300 WM is also 1/2x28. 5/8x24 covers most 6mm, 6.5mm, 7mm and 30 caliber and even some 338 calibers, such as 338 LM by Christensen Arms which is 5/8x24. It’s best for you to consult your firearm maker to confirm which thread pitch for your particular model.