No idea. But the same springs are sold in several different versions. I have upgraded to Townshend but originally used these from Nobsound https://www.amazon.com/Nobsound-Aluminum-Speakers-Isolation-Amplifiers/dp/B07K9ZYP84/ref=pd_lpo_23_t... Check out nonoise I think it was he had a big Nobsound thread a while back, bunch of people had great results with them.
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