500 Jacobs Rubberflex For L-0 Spindle COLLETS, 501 - 510 Collets JACOBS RUBBERFLEX Collet Chuck for L-0 Threaded Spindle Nose
an L-O spindle nose is just under 4-1/2Inch Dia Threads & 6 TPI
L0 is a very common size for LeBlond Regal lathes
Takes from .100 to 1.06Inch.....