Ltd 550 stock handle bar size?

Just need to know what's the stock handle bars size. Not sure if it's 1 inch or 7/8.....thanks

7/8ths.

What would be the size for 79 kz400?

The same --- many KZs have the same handlebar clamps & grips.
Most if not all Japanese motorcycles of the era were probably 7/8.
The later V-Twin cruisers probably have 1" bars or something like that.