Get a new rigger!
aren't the same size,they are close, and may work, but absolutely not the same size. And any decent rigger should know better.
Swagging relies on the parts
cold forming (or cold welding) together to form a continuious mass of steel
to function properly, a mis-sized part can do one of two things.
1) doesn't allow for enough compressive force to properly form the parts together, which will allow free space in the swag. This can allow eithe the roots of crevice corrosion
to take over and destroy the part, or for the two parts to slip past each other under load and separate.
2) over compressing the part, which can cause micro fracturing of the part, and will lead to premature failure.
If he insisted it will work, ask for the manufacturer of the parts he is using, and call them to ask if they will stand behind a warranty if it's done this way. I don't know of a company that will (we certainly won't).