Well... I am still new to this company, seeing as I have been here for almost 2 months. I wont be able to describe it as well as some of the other employees, but I will do my best.
The RO# is basically the request order number. This can only appear once, which makes it a good canditate for a PK.
The JCS# is basically the number for the shaft that is being made. It symbolizes the size, the parts used and everything else. This one should be the PK for the BOM (bill of materials) because it makes referencing it much easier. Each JCS# has a specific set of parts, construction notes, and labor hours that go with it.
The shaft# is the number of the shaft being made (or inspected). Any BOM can have any number of shafts that go with it. as an example, Ford could order 7 JCS# 000.0000.00.0000.000.00's, and each shaft will have a different number based on a few things, which I still dont understand fully.
When we go into the files to find a part, we always look for JCS#, its basically like OUR part numbers for shafts (if that makes sense). We dont look for RO, or shaft numbers.
When we do inspections, such as with the WORKSHEET FOR DYNO SHAFTS, we often inspect several shafts, so we use the RO# as main reference, and then the shaft# for each set of readings of each shaft in the RO.
I hope this helps and its easily understandable. Let me know if I should clarify more.