This is the http://www.thermikUSA.com Rambler mug handle. It essentially convert your Rambler 20 ounce or 30 ounce into a mug. It is made of heavy duty plastic which seems pretty much impossible to break from my testing.
The unit slips from the bottom to the top and it hold your Rambler (and other mug with similar shape I might add) in a perfect mug shape handle.
Though the stainless steel insulated rambler works great it’s quite slippery. I know I have dropped my rambler a few times. With the Thermik, you can carry it around with one finger.
The only draw back I have came across is that with the handle installed some cup holders will not work with it. The handle is easy enough to remove so it wasn’t a big issue.
The product sells for $12.99 on Thermik USA and they come in about 6 different colors.