You're purchasing a single timer knob, stripped from Drucker brand centrifuges returned as not needed/wanted, or not functioning (usually a crap-tastic timer or motor was to blame). If you need more than one knob, I have other listings selling them as pairs or in lots of 5 or 10 (mainly so you don't get slammed with too much shipping charges). These were harvested before COVID existed and have been stored indoors in my home.
This knob also fits the timers on Hamilton Bell V6500 centrifuges. I've included a shot of the alignment of the flat side to the dot on the knob (seen in reflection). Please make sure this is the proper alignment for your timer.
If you want any plastic spacers ("top hat" design for a metal chassis, thick o for a plastic chassis), add a note with your purchase, or send a message. Otherwise, the knob will be shipped without spacers.
After the ebay fees and my stripping/handling fees (these centrifuges don't strip themselves of parts, you know!) the remaining 75% of the proceeds of this sale go to my favorite non-profit organization: my local chapter of Sweet Adelines International. I thank you, and the Chorus thanks you!