JOWO 6 Steel SOFT nib unit

Steel nib unit with ABS plastic feeder and threaded housing. Optional ebonite feeder.

Size 6, that means that the feeder is 6 millimeters in diameter. 

Thread housing M7.4x0.5, but the tap to make the  grip section thread is M7.5x0.5 

A drawing with dimensions can be found in the las picture of the gallery in this product.