We had our contractor install these slides in our 20 year-old cabinets and we are very satisfied with the result. The drawers now extend all the way out and have the soft-close feature found on newer cabinets. Definitely worth the cost.
I used a pair of these for a trash/recycle cabinet that I built, with a pull out drawer. Heavy duty rating seemed more than enough for what I was using them for.
I do paper crafts and needed a drawer to hold my 12x12 paper booklets that are incredibly heavy. My husband built it using these and it is fantastic. No more back strain lifting the paper.
Willard E. Holland Jr 
