I was going over the BOM for the McWire and noticed that McMaster no longer carries the 4" spring specified. See below. They suggest a replacement that is weaker at 1.22Lbs/IN. Does this make difference? Or should I look for a closer match to the original at ~5Lbs/IN?

9654K167
Steel Extension Spring Zinc-Plated, 4" Length, 1/4" OD, .032" Wire
This item is no longer available. We suggest:

9654K207

Differences:

9654K207
Rating: 1.22 Lbs/IN

9654K167
Rating: 5.32 Lbs/IN
This product is sold in Packs of 6

As I understand it, the springs are there to hold the bearing arms against the tracks, so as long as they can do that you should be fine. I got the K207's and they seem to be doing an admirable job... but of course I haven't got my Repstrap hooked up and moving yet, so I don't know how they perform while actually moving.

Elastic Bungey or Shock cord could be an alternative if you are still struggling sourcing springs.

aka47

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Necessity hopefully becomes the absentee parent of successfully invented children.