You need to copy this to a special Fusion folder. You'll find official instructions here.
Unfortunately next time Fusion is updated your custom thread files become 'orphaned' and left behind as the thread folder is changed. However, there's an add-in called ThreadKeeper which manages this and moves all your custom threads to the new folder when Fusion receives an update.
Hope this helps.
ps I'm off to bed now as it's getting late here in the UK. If you have any questions I'll try to answer them in the morning.
If this answers your question please mark the thread as solved as it can help others find solutions in the future.
Marcus Wakefield
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I've created a Windows application (and now Mac as well) for creating custom thread files for Fusion. You can find out about it here. Hope you find it useful.
If you need to know how to offset threads for 3D printing then I've created a guide here which you might find useful.
If you would like to send me a tip for any help I've provided or for any of my software applications you've found useful, you can do this via my Ko-Fi page here.
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