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Knitting needles and needlepoint items including scissors under four-inches are permitted in your carry-on bags. However, circular thread cutters, or any cutter with a blade must be packed in your checked baggage.
Per the TSA:
In general, you may place your knitting needles and needlepoint tools in carry-on or checked baggage.
Circular thread cutters or any other cutter or needlepoint tools that contain blades must be placed in checked baggage. You are permitted to keep scissors smaller than 4 inches in your carry-on baggage.
Even if an item is generally permitted, it may be subject to additional screening or not allowed through the checkpoint if it triggers an alarm during the screening process, appears to have been tampered with, or poses other security concerns. The final decision rests with TSA on whether to allow any items on the plane.
So in short, don't bring any heirloom needles, and the more benign ones the better (plastic, for example).
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