Here is the Ultimate explanation of Strap fitting
What size strap do I need for my Panerai Watch?
For your 40mm Panerai watch you need a 22mm width. For a 44mm Panerai you need a 24mm strap. And for a 45 or 47mm Panerai watch you need a 26mm strap.
The second number i.e. 24/22 or 24/24 is the width of the strap at the buckle. A 24/22mm has a slight taper and fits the Panerai OEM buckle as well as many of the TC buckles. A 24/24 needs a 24mm buckle or, quite usually, these non-tapered straps have a sewn-in buckle.
What length do I need?
The OEM Panerai Straps are 115/75 in length. 115mm on the side with the holes and 75mm on the buckle side.
Look at the bottom of your wrist and see where the buckle sits....if it is in the middle then 75mm is your size....if it is off to one side...measure how much more or less you need and add or subtract from 75mm 8mm at a time....8 mm is usually the distance from the middle of one hole to the middle of the next.
On the long side, which hole are you in? If you are in the first, second or third hole from the pointed end you need a longer strap. Some people use both keepers to help the strap and some prefer one. This will determine what length is best for you
Can I use any strap on my Deployant buckle?
Straps are usually 4 to 5mm at the watch case and on a deployant strap they get thinner, down to 2mm at the buckle so they can fit in the slot. A regular buckle stays pretty much the same thickness throughout and needs a tang buckle.
You can use a depoyant strap on a tang buckle but you cannot use a regular thickness strap on a deployant buckle.
