These skates are engineered and made with pride in USA.  
Each set includes 4 machined and matched skates assembled and ready for work.  
Most likely the leveling screws on your machine will afford you sufficient room to install them without the need for toe jacks or other expensive machine moving equipment. Each skate is drilled and tapped with 2 holes at 1.50 spacing (1/2 x 13UNC) for permanent mounting to any heavy machine, cabinet, table, etc.  
The block is manufactured from solid machined aluminum and fitted with 6 wheels. Each skate is fitted with 6 new cam follower bearings with a working load rated at 2225 lb. each and static load of 3060lb (CCF 1-1/8 SB-SV1 .00). The bearings are "O" ring sealed with needle roller bearings and lubricated for life.  
The skates have a 30% overload factor, in normal conditions use 4 skates for machines approximately 10 ton and use 3 skates for machines up to 15 ton. (Yes, it is correct- 3 skates will carry a heavier machine if the floor is uneven.  Why? Because with 4 skates an uneven floor will place all the weight on 3 skates).  
Specifications  
Overall length: 3 5/8 inches  
Overall width: 3 3/8 inches  
Height: less than 1.25 inches  
Weight: 1.65 lbs. each  
Maximum load: 10,000 pounds each