METAL STEM & Screw thro bowl
Upper image presumably the earliest Kirstens, stamped 'PATS APPL FOR - S'
(Upper pipe) and 'PATS APPL FOR - M'. Neither pipe has O rings.. the S stem is 3 1/2 inch long and the M is 3 3/4 inch
Centre image shows the variations on valve and bit
pats & pats pend Made in USA S stem length 3 3/4 inch
pats & pats pend -L stem 4 inch
pats & pats pend - A stem 4 1/2 inch, the longest Kirsten produced
none of these three has any O rings