It seems that a small number of saws were made with a rod that has a non standard thread size so please check that the thread on the end of the rod is an M8 1.25 (take the rod to a hardware store and try screwing on an M8 1.25 nut) and the exposed shaft must be at least 18mm long to ensure the knob will fit. Please note that the actual color may vary and may be black, gray or orange.
If you need to purchase a miter lock knob for the Ryobi TSS101L please see my listing here:
https://www.ebay.com/itm/115687917613
You can purchase both the miter lock knob and the bevel lock knob as a discounted package here:
https://www.ebay.com/itm/115224944259
I also sell the bevel lock knob which you can purchase here:
https://www.ebay.com/itm/115220033683