Henry rifling is most commonly associated with the British Military single shot rifle the Martini Henry and in caliber .577/450 Martini.

In the MH the rifling is seven flats and seven peaks. The center of the flats is the same diameter as the top of the peaks.(Minor diameter)The corner of the flats where they meet the bottom of the peaks is the major diameter.

The MH is a bit complex and I won't get into it unless you wish. It is a partially tapered bore and is not a .458. It takes some special understanding to make the MH shot. If you want more info on this bore let me know. There are some tricks like how to slug and measure the bore.

Many commercial .45 Henry barrels do not have the over size measurements of the MH and are true .458 45's.

Westley Richard also used Henry rifling of 9 flats and peaks.

Need any more help with this just ask.

I thought I had some bore pictures but all I could find was this "colorized" version.

The dark lines are the peaks and the flats are in between.