Note: Rail mounting holes for M3 (6x4.5x3.5) and M4 (7.5x5.3x4.5) are available for MSB15 rail. The codes of rail type are MSB15R for M3 mounting holes, and MSB15U for M4 mounting holes.
The basic dynamic load rating C of ball type is based on the 50 km for nominal life. The conversion between C for 50 km and C100 for 100 km is C=1.26 x C100. 
Single (Single carriage) / Double (Double carriages closely contacting with each other).