Knob for Rear or Front Wheel Assembly, 2 Pack. Replacement Rollator Parts.
For the Medline Steel Rolling Walker Rollator MDS86850ESKD
NEW. MEDLINE brand. SHIPS from California, USA
  • This knob is for the WHEEL ASSEMBLY, it is 1/4 " SHORTER than the knob used for the height adjustment of the HANDLE BARS

It is usually TOO SHORT for the HEIGHT adjustment of the HANDLE BARS
Diameter 15/64 " 
Total length 1 7/8 "
Length of the metal section 1 1/4 ", as shown in the picture

There is another listing of a knob like this one. They are both from Medline and for the same purpose,
This one is just 1/8 " longer than the other