Hi, my name is Ryan. My family has been selling outdoor power equipment since the 50s.
The part number MTD 720-04123 is a wing knob (1/4-20 thread, approx 1.73″ length, black). 
Here’s what that means and how it’s used:
⸻
✅ What it is
• A wing knob, sometimes called a wing nut or wing-bolt style knob, that you grip by hand (wings on the sides) to tighten or loosen something without tools. 
• Thread specification: 1/4-20 (¼ inch diameter, 20 threads per inch) size. 
• The original part 720-04123 has been superseded by part number 720-05066A. 
• It’s used on various push mowers (walk-behind / push type) from brands under the MTD umbrella (MTD, Craftsman, Troy-Bilt, Yard Machines, etc.). 
If there is a question of this wing nut, fits your unit please message me or respond quickly and ship the next day
Thank you
Return Policy
FOR ITEMS THAT SAY RETURNS ACCEPTED, THE FOLLOWING APPLIES:
* If you are not satisfied with your purchase, we will gladly exchange it or offer a refund (excluding shipping).
* If the item was shipped FREE the actual cost of outbound shipping will be deducted from refund amount.
* Once you place your order it can not be modified, changed, or canceled.
* Any returned Items must be sent in original condition, box and with all received documents or invoices. Buyer is responsible for return shipping cost, No Exceptions.
* Returns must be in resalable condition. If the part is used there is a possibility that you will not receive a refund, as we cannot sell a used item.
* Electrical parts are not returnable.
* Any damaged or defective items or items which do not match item description will be replaced once damaged item is returned to Bidds