Johnny Ringo wore a very distinct spur strap in the movie "Tombstone".  It was authentic to the times.  I will offer my reproduction of it here.

If you are making nonadjustable, single-hole, spur straps, you can measure from the center of one spur button to the other, over the boot.  It would be best if the foot that was goin' to be in the boot was there at the time.
I have traced my pattern and rough-cut around it.  I'm not goin' to trim it out till I'm done with the carving and stamping.  This will help limit the distortion that occurs when workin' narrower pieces of leather.

Here, you can see I've already incised my leather design.

This spur leather is set up for 10 inches, but the pattern will have options for different length.
Here is a close-up of the incising for the rosette.
The first stamping tool used is the C830 Camouflager.
The next tool is the P703 Pear Shader.

Then, I use the B701 Beveler.  You can see the use of both these tools in this photo.
This shows the use of the Beveler around the inside edge of the diamond-tuck pattern on the main body of the spur leathers.
The next tool is the V708 Veiner.  You can see how it is used here to accent some of the existing incised cut, as well as create texture.
In this photo, I have added the minimal decorative cuts, and accented the inside corners of the rosette with the A117 tool.  I always call it a pointed Beveler, but it was intended as part of the Backgrounder tool selection.
The A117 tool is also used in the upper and lower points of the incised diamond pattern to create the "tucked" look.
This is what she looks like after tooling and trimming the spur leather to its final shape.  Any distortion from tooling can be minimalized with the trimming process.  A 1/4" punch is used for the spur button holes.
I find it helpful to trim out a little on the back side of the spur button slot.  Nothing will make getting the spur buttons through the leather easier, except a longer slot.

Feel free to make a bigger cut than what I allow in the pattern.  As the spur leather gets old, I prefer to have that extra security of a shorter slot.
Once I get the buttons through the slots in the spur leathers, I never take 'em out.  I slip the whole shebang onto the boot before I put it on.  It works well for me that way.

I will be dying these leathers black, but I wanted to show them on the boot before dying them so the details could be easily seen.
These can be worn with the point on the inside or the outside, depending on your personal preference.

In the movie, Ringo wore the decorative rosette carving on the outside and the point on the inside.

I like the point on the outside so when it gets curled-up with use, it doesn't get in the way of my other foot.
Just a little bit of time in the rust tank, a quick rub of Kiwi Black Shoe Polish, and they are done.