I needed to replace a bunch of side knobs for the 24-inch fans at work. I printed them in PETG with supports using support filament for a clean removal. The threaded inserts are M8x10x8 with a 1.25mm pitch. I used these:

MroMax M8 Knurled Insert Nuts, M8x8x10mm Female Brass Knurled Threaded Insert Embedment Nuts Metric Thru-Threaded Pressed Fit into Holes for 3D Printing Injection Molding Gold 100Pcs: Amazon.com: Industrial & Scientific