The description says "for 33mm plastic nuts". The ring nuts may be 33mm, but there is clearly no cap. I assume they are about 45mm, the diameter of this product. Truck drivers may know this. But not others. I actually bought this to help install a faucet in my kitchen sink with a large 33mm nut. The chart shows the measurement correctly. But I didn't feel the need to look beyond the description, which seemed perfectly clear. I returned it.