1979 KZ750B twin exhaust pipe diameter

Is exhaust pipe o.d. nominal 1 1/2" or 1 5/8"? My digital calipers show 1.59" actual. Wondering which nominal size mufflers to order. Would 1 1/2" have enough slop? Would 1 5/8" have too much slop? Thanks.

If your calipers show 1.59, then 1 1/2 would not fit.
I believe 1 5/8 then...

Good luck.

Does design of new muffler rely only on a snug slip-on fit, or is it held with a ring clamp?

Shimming and/or hi-temp sealant may be feasible with a slightly oversize ring clamp version.

Where snug slip-on is desired, a muffler shop may likely be able to expand the muffler to a perfect i.d., (which is the ideal solution to V&H muffler>header fitment, and doesn't affect the plating on a chromed V&H muffler).

But too much expansion might crack chrome plating in other applications.

Good Fortune!