To the OP – I think you've read the drawing wrong.
Try NBSC: New British Standard Channel, followed by the section number.
The drawing I think you're referring to says NBSC13 – 10" x 3 1/2", as shown in the Dorman Long handbook page 41 here: **LINK**
On page 60 you can find details such as the taper angle of the flanges and the section thicknesses.
If it had been an 'I' beam, it would have a NBSB reference, equal angles NBSEA, and so on.
Andy