sentences:  Originally invented by Fifty-50 (an aggressive inline skate frame company), Juice Blocks allow the skater to convert their flat or anti-rocker frames into proper freestyle frames.Juice Blocks are simply solid grind blocks inserted into the axle holes where two middle wheels or anti-rockers are found.Tri-rocker (not to be confused with the 3-wheeled frame/chassis seen on Tri-Skates) is used by some aggressive skaters.