Danny D. wrote, on Mon, 29 Sep 2014 05:36:57 +0000:

Another question I have is what are these "20" numbers indicating that
are stamped on the chain on the metal "iceberg" parts below the
waterline?
https://c3.staticflickr.com/3/2947/1...74301fa4_c.jpg

Since nobody answered, I just called Oregon chain customer service again,
at 800-487-5951, who explained the "20" stamped on the Oregon H72 chain
indicated that it is a "Type 20" drive link, which, if you have the
secret decoder ring, corresponds to a 0.325" pitch, and a 0.050" gauge.

The weird thing is that this new representative, named "Becky", confirmed
that the Micro-Lite bar that I have does not take an Oregon H72 chain,
but it takes the Oregon G72 chain, both of which have the exact same
pitch, gauge, and number of drive links.

The only difference is the cutter.

Anyway, when I looked at another of my older chains (maybe the original?
), it had a "30" stamped on each of the drive links, which, Becky told
me, indicates an H30 micro-lite chain, with the smaller cutters.

Some diabolical epiphanies that come out of these conversations a
0. Knowing the pitch, gauge, and drive links (apparently) isn't enough!
1. You also need to know if the bar is designed for smaller cutters!
2. The Oregon G72 & H72 chains have the same pitch, gauge, & drive links.
3. But only the Oregon G72 fits my Micro-Lite bar (thinner rails?).
4. The 20 or 30 stamped on the drive links indicates an H20 or H30 chain.
5. I can *find* the drive links by looking for that specific stamp!
6. There are two kinds of sprockets, but I apparently have the "spur".
7. A chain with 62 drive links will chatter & damage the sprocket spurs.
8. The H30X-72 chain costs about $35 if I have Husqvarna ship it to me.

The only inexplicable thing that comes out of these two phone calls are
that a chain of the exact same pitch, gauge, and number of drive links
can be different in cutter dimensions, such that it won't fit a standard
bar.

I find that confusing because the Oregon package doesn't say what both
the Oregon (800-223-5168) and Husqvarna (800-487-5951) support personnel
say.