The stamping can confirm whether the cylinder has a standard taper at the top. 

Here's what the stamping means:

TYP 17-4  Standard Top Taper - All of our cylinders have this taper. (if your chair is from a big-box store or manufactured after ~2000, it's 99% likely you have a standard top taper)

TYP 17-2  OBSOLETE Taper - must replace the mechanism and gas cylinder.

TYP 17-26  OBSOLETE Taper - must replace the mechanism and gas cylinder.

And the things to ignore (defined for inquiring minds):

DIN 4550  (ignore) Global Standard   (a "-3" or "-4" afterward indicates the Class. See below if interested)

CLASS 3  (ignore) Piston Wall Thickness related - Class 4 is best (ALL chairpartsonline cylinders are Class 4 - Only the BEST!)

CLASS 4  (ignore) Piston Wall Thickness related - The thickest walls #Best

BIFMA  (ignore) Furniture Testing Standard