In 1998 there was a change in the castings for Source Four Barrel Assemblies that necessitated a change in the 19 degree lens. Therefore a 19 degree lens manufactured before 1998 won't fit in a modern lens tube, and vice versa. Details are below.
The Old-style lens tube was used before October 1998.
The New-style lens tube has been shipping from October 1998 forward.
Old style 19º lens part number is 7060A4002 and is 112mm (4.48") in diameter. It is no longer available in the US.
New style 19º lens part number is 7060A4077 and is 128mm (5.12") in diameter.