What "Heavy duty" means ?

This means those articles are made with thick main leather straps (on top), tested and approved for hard play (bondage, pulling, but careful this is not made for lift or suspensions)

The thick leather parts are made with 2.5-2.8mm thick vegetable tanned leather (tanned with natural products), this gives to the leather the natural smell and small defaults on it, i dont use pure zéro default leather you can always see the skin texture and small details on it, 

the lining is made with high quality mineral tanned leather (tanned without high chemical products like chrome or mercury)
from italian, spanish or french tanneries, this leather dont need grease, just clean it with leather soap after a long use, 

the hardware (rings, rivets and buckles) needs also a bit of care, especially against sweat, the sweat is very salty and bad for lrather or steel without cleaning, always keep care of your goods and they will looks always good :)

Some examples bellow