I'm not sure what these markings mean. I've seen them on some but not all JK necks. They always play quite well and this one certainly does. The neck measures at 24.7mm on my calipers.You may get a slightly different reading and it may need modest sizing up or down for a perfect fit. The item "Keilwerth JK SX-90 SX-90R series Alto Sax Neck. Stamped 5 on the tenon" is in sale since Saturday, May 23, 2020.
This item is in the category "Musical Instruments & Gear\Wind & Woodwind\Band & Orchestral\Saxophones". The seller is "jwsaxophone" and is located in Quincy, Massachusetts.
This item can be shipped worldwide.