EFL is the effective length of the belt
It is the system used in the EU so they can be different to the USA ( outside length ) & old Commonwealth countries ( inside length )
And yes they are inches
So in most cases you would fit a US 100" belt if the pulleys are all in good condition or a 99" belt is this in on an old warhorse
Belts are not all that accurate and often the size is actually wrong
Belt makers all have apps for the designers to pop pulley sizes , speeds & loads into and it spits out idiot lengths & tensions like 254.165"
The mower companies publish these lengths to diswade owners from fitting standard size belts for 1/3 the price.
They also change the belt V angle which may cause standard size belts to wear rapidly
AYP at least generally use standard section belts
MTD belts are generally slightly wider so std belts really don't work particularly well .
Thanks for that information. It is also discouraging that belts sold at auto parts stores in my area (Auto Zone and Advance Auto Parts) have no marks on the packaging that correlates to the size, length, width or type of belt. It's a simple part or item number.
Prices for similar belts in my area from auto parts stores sell for around $40. Genuine Husqvarna belts I found on the 'net range from about $70 to $35.
I finally broke down and ordered a genuine Husqvarna belt from a Michigan supplier for $35 but it will probably be a week getting here so I guess I'll be push-cutting my lawn with a twenty-inch mower in the morning.