The control surface PCBs are designed to work with the following parts:

863129Drehknopf DK16-190V3 A.6/4,5 AT=14 schwarz soft-grau 1677498
863120Drehknopf DK16-190V3 A.6/4,5 AT=14 schwarz soft-rot 3092
863118Drehknopf DK16-190V3 A.6/4,5 AT=14 schwarz soft-weiß

Do not email ALBS.de and try to order just 15 knobs, they may ignore your email. There are bulk orders arranged on the MIDIbox forum for these knobs. If you missed out on a bulk order, start one of your own and get orders for at least 100 knobs before emailing ALBS.de.