Description from Otter Creek Labs:

"The Polonium is made to be a quiet, duty rated, hard use 5.56 suppressor and is offered in both standard and K length options. If you’re looking for the best size, weight and price to sound performance ratio on the market that you can beat the absolute crap out of then look no further than the Polonium series. We don’t need to make up fake, fancy marketing language or give you padded/deflated dB numbers taken on subpar equipment – the reputation, performance and track record of the Polonium and Polonium-K speak for themselves.
 
The Polonium uses a 6mm bore that is also compatible with any 6mm/.243 cartridges and has a highly effective built in internal and external flash hider that offers superior flash reduction over the competition when using night vision or when shooting in low light conditions. The unique look comes from external weight reduction, removing all unnecessary material to keep the weight down but still as strong as possible. This results in a suppressor that has 10% more surface area depending on the length that will shed heat and cool down quicker.
The Polonium and Polonium-K features industry standard universal 1.375×24 rear threads so you can pick what mounting system best fits your needs."