So, if you have not figured it out yet, Oregon uses letters to designate chains sold through consumer channels - hardware stores, home centers, etc. This is to simplify things for consumers instead of trying to teach them about pitch, gauge, cutter types, and drive link counts.
S = series 91, 3/8 low profile pitch, .050 gauge chain
R = series 90, 3/8 low profile pitch, narrow kerf, .043 gauge chain
H = series 20 BPX, .325 pitch, .050 gauge chain
J = series 21 BPX, .325 pitch, .058 gauge chain
L = series 22 BPX, .325 pitch, .063 gauge chain
G = series 95V, .325 pitch, narrow kerf, .050 gauge chain
D = series 72V 'Vanguard', 3/8 pitch, .050 gauge chain
'S56' is type S chain (3/8 low profile, .050 gauge) in a loop with 56 drive links. 'S60' is just a longer loop.
Since these are consumer oriented packaging, they are typically low kickback style chain, and usually, but not always, semi-chisel chain, as that makes the most sense for that user. If you want other styles of chain, you have to step away from the letter coded packages.
You can also order chain through saw shops or catalogs using the Oregon number, or the equivalent STIHL, Carlton, or other brand identifier. Or in your case, simply state that you want 3/8 pitch, .050 gauge chain and the type of cutter (semi-chisel, full chisel, skip tooth, etc.).
Back to your D70 / D72 question.
1. It depends. Sometimes when you buy a replacement bar from a third party it uses a different number of drive links than the bar that the manufacturer supplied. My Echo saw came with a 57DL chain, instead of the more commonly available 56DL used by lots of other saws. Can't get a 56DL loop to fit on the Echo bar to save my life. The replacement bars sold by Oregon are 56DL bars. If I buy an OEM Echo bar - 57DL. I assume that this is to get me to go back to the Echo dealer?
2. It's possible that someone looked at the number stamped in the drive links of your chain and got confused. 'D' type chain is also known as 72 series 'Vanguard' chain and has that number stamped into the drive links for identification.
Bottom line - you need the correct number of drive links for the bar you are going to use, not necessarily the bar that the manufacturer supplied with the saw.
Philbert
