LEGO Technic Axles - Choose Length & Colour (Packs of 4) Design 4519, 3706, etc. | eBay
LEGO Ruler and Sorting Tool - Tom Alphin
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LEGO® 32073 4211639 - 32073194 - ToyPro
Lego 6 Black technic axle 6L or 1 7/8 inch length | eBay
Missing Lego Brick 3706 Black x 4 Technic Axle 6 Studs Long 370626 | eBay