ZRM&E 20PCS 1/4 inch x 20mm Threaded Insert Nuts with Hex-Flanged Washer for Wood Hex Drive Head Screw-in Type Furniture Embedded Screw Plug: Amazon.com: Industrial & Scientific
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1/4"-20 Int Thrd Sz, 51/64 in Overall Lg, Hex Drive Threaded Insert - 4ZU96|4ZU96 - Grainger