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We've been using Jack's Machine Shop as our supplier in the U.S (They won't ship outside the US, if you are aware of a machine shop located outside the US, especially one in the EU, please get in touch with us!). The last time we ordered from them, they charged around $11.00 per piece for a quantity of 100.
Design variants
there's multiple designs, early springs with wide heads (v1.0), these work well but the heads of the springs are a bit too wide and can intresect. To avoid this, simply cut the sides of the heads down with scissors. It might even be useful to remove one of the sides of the head.
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