Right, the spring is adjustable. That's why there are actually two 5/16 nuts, where the coil & condenser wire attach. The innermost nut is loosened and spring can be moved fore and aft as required, then re-tightened to achieve the correct spring tension. On Fords the specification for V8 is 17 to 22 ounces, checked with a spring scale.

Likely, few are aware that there is also a wide variation in spring tension specs., even with NOS USA points. Too much, and the rubbing block wears down quickly, changing the timing/gap. Too little, and the contacts float at high rpms. Had to test quite a few sets to find good ones.

6 VOLTS/POS. GRD. NW INDIANA

STANDARD OR ECHLIN.  Make sure the box says "Made in USA".

Where do you find NOS points?

Distributors are amazing considering how old they are.  I remember years ago when a local speed shop offered to curve your distributor for $10.  The guy doing the work said he could give anyone a 10th of second ET decrease for $10.  $10s a tenth is what he said.  My smart ass buddy walked up and said he would take $100s worth.  We thought it was funny, the distributor guy didn't. 

You get one guess.

The counterfeit condensers get lots of bad press with good reason, though keep in mind the points included with them these days aren't much better. They should be avoided.

The genuine service or NOS replacements are still plentiful and inexpensive, better made with better materials. The thing about ignition parts, while they may work, that doesn't necessarily mean they are working anywhere close to where they should be.

While you're picking up condensers suggest you find some NOS point sets as well. Still have the old set I ran for quite a while years ago. I wasn't aware then, the distributor cam needs a bit of high temp cam lubricant, so the rubbing block on this set is worn down to a nub. The better made sets use phenolic, not plastic. The el-cheapos will wear down right away cam lubricant or not.

Assembled a complete spare distributor to carry on road trips, just in case the Pertronix were to fail. The idea is to drop a spare distributor in and be on our way with minimum hassle. This is why I lean toward including a modern capacitor. The NOS automotive condensers test OK now but may not work when needed.

Part of setting up the spare is learning (or re-learning) the rituals now, in my garage, instead of on the side of the road.

And I gotta say it's pretty amazing all the contortions people use to have to go through. For one thing, if they sit a while esp. in high humidity, points will get a layer of crud between them that will absolutely kill any continuity. You think "hey I cleaned 'em.", Nope.

The distributor design is an amazing piece of engineering for the time though. Everything ignition related today is handled by sensors, software and computers, they had to make do with the technology they had - springs, weights, & gears, and overall do a great job when setup right.

I bought a rebuilt YBlock distributor last year for my TBird.  The condenser failed within a few days leaving me stranded.  I went to my local O'Reilly's and asked them to sell me quality US made points and condenser.  They've been in my car ever since. It's a good thing the Chinese don't make condoms (do they?) 

Sounds like it's NAPA Echlin or from Ford. I don't think I will go down the path of installing an electronics type capacitor.
Lots of interesting information, though some beyond my understanding.
It brings back memories of when I was doing a pre-apprenticeship in auto electric. We would charge up condensers and throw them to the mechanics to catch.
Thanks for the tips on brands to buy.

Interesting. I can only assume the ‘quality of the spark’ is irrelevant if the plugs never misfire under load (?). (either the mixture explodes on cue, or it doesn’t). Same with the contact points. If they continue to function perfectly past the life of most other ignition components, the degree of pitting or burning would also seem irrelevant.
P.S. This brings up another controversial issue, namely whether positive ground system contact points pit & burn at a slower rate than negative ground examples. Also reduced advancement of body ground connection corrosion in pos. grd. systems is debated (?). Seems a largely unexplored subject unfortunately relegated to ancient history.

6 VOLTS/POS. GRD. NW INDIANA

No idea on that, it's just something I observed, that some of these NOS capacitors on hand have lost this characteristic (that they would have had when new) although, they test OK under high voltage for leakage. The voltage is bleeding off somehow, in seconds, versus hours or days compared with a new capacitor. This is known as the "insulation test".

It might be they will "work" though would prove defective when looking at the ignition pattern waveforms on a scope. A multimeter works OK for measuring capacitance value, but it can't test for leakage at the working voltage rating

The condenser plays an important role in the quality of the spark at the plugs as well as preventing the contact points from pitting or burning.