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M4 Friction-Knuckle Helping Hand Arm Link
A stackable link for building your own soldering helping-hands arm. Each 71 mm link has a flat M4 tongue at one end and a 90°-turned fork at the other, so a chain of links alternates between two joint axes. Each fork has a 6.3 mm gap for the 6 mm tongue, a 4.5 mm M4 clearance bore and a hex pocket that holds an M4 nut (7 mm across flats), so an M4 x 20 bolt tightens each joint to set its friction. Two zip-tie slots in the bar strap an alligator clip, magnifier or probe to the last link.
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