SWIVEL Knob Spindle - Pin one end/threaded other Stepped Spindle 5.25"

Description

Early 1900's door knobs were made from wood, cast brass or cast steel. During the war years, knobs switched from cast brass to cast steel then stamped steel due to material availability.
Customers  insisted on the brass look, so manufacturers started using thinner brass material and spun two pieces of stamped brass together. The look was similar and this opened the door (no pun intended) to fancier face designs on knobs by embossing knob components when stamping.
Door knob spindles evolved as well (see vintage YALE and RUSSWIN catalog pages attached).
This item is close to a YALE 1168F - see picture enlarged to show detail and dimensions. These, however, are 5 1/14" double swivel with stepped shaft. You know it when you see it as the lock has a pivot point to accommodate the larger square shaft as well as the more standard 9/32" smaller square hole.  Threaded end  is .28" square and accommodates a 3/8-16" tapped hole in the knob. See pix.
Designed and used primarily for schools, hotels and motels for extra security. The locks had a "split" pivot for the spindle that was also considered a split spindle. meaning the exterior knob was usually rigid and the interior knob operated the latch as well as the cylinder lock. CORBIN had many types and styles of large locks with the split spindle hub (3/8" x 5/16").
If you need a rigid spindle to accommodate the lock, then buy one or more of these to suit your needs, have the spindles tack welded (as they are steel), grind them down to fit and use as a rigid spindle. The lock will function with exterior and interior knobs working. The last pix shows a 1941 CORBIN lock catalog page showing the type of "hotel" lock with an explanation of operation using this spindle (hub as they refer to it).
Lock manufacturers (seeking ways to differentiate their products) switched to odd-ball thread sizes like 3/8-14, 9/24 etc. so measure thrice, buy once when buying threaded knobs and spindle hardware. If questions, please send email.