Down here Pix belts are distributed by Jack Max who are the bottom end cheap imports wholesalers.
I did have an account with them but I no longer do as very few of their product lines where a direct replacement.
When I started belts were my biggest nightmare particularly as we measure the inside & you lot measure the outside.
As Hammer stated there is a lot of variation, particularly with the size of the kevlar chords & their placements.
Now I use Stens, Rotary, or Oregon belts and when I come across a size that my suppliers do not have the I buy a Gates blade runner lawn & garden belt ( numbers start with BR )
All of these are from the OEM Exact replacement series and not the general V belt series .
'Then when it comes to MTD vari drive belts, it is often original MTD belts only.
Usually you can not substitute a deck belt for a transmission belt & visa versa because the kevlar chords are different sizes in different positions , regardless of the actual belt dimensions.
Clutching belts ,as used on transmission & manual PTO must be wrapped because as the rubber gets hot, it gets soft & sticky.
Try this yourself when you get out of your truck, flip the hood and grab the belt , feel how sticky it is which is good on a water pump / alternator belt because you do not want it to slip .
However on the mower you do want the belt to slip when you are clutching or starting / stopping the blades so these belts need to be wrapped to hold the stickyness inside.
You can verify this by reaching up and grabbing the transmission belt when you have finished testing the next mower, it will be hot but not sticky.
Then you get to the wraping material.'
It can be cotton, Kevlar or pollyester and each one will act differently on the mower.
Also never ever trust the size written on either the belt and in particular the wrapper.
The belt factories supply the wholesaler with unbranded belts usually in boxes of 100.
The wholesaler then puts the lables on them and it is not uncommon to find one marked wrong.
The exception to this is MTD where the belt number is moulded into the belt .
My go to for checking belts is Gates and this is the web page I use
Gates belt interchange catalogue.
You type the mower belt number in the lower window.
In this case I used
754-04118 which is the belt for the yardman I am still struggleing with
The result was 6777BR
If you click on the BR number
You bring up the Gates catalogue 6777 BR specification
And scrolling down will bring up the exact specifications
In this case it is an A 121 63/64" USA size with a 1 deg smaller V angle than the standard 40 deg
Most aftermarket belt suppliers will supply a 122"
If you fit a standard 40 deg belt, you need to run the belt a good 1/2 hour to bed it in to the pulleys
