The "lines" on this brass end cap represent another form of knurling known simply as "straight knurling", if my memories of cold metalworking industrial arts classes are correct.
Engine lathe work done at slow speed.
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Captain David Longenecker, CFI, CFEI
Fire Marshal, LCBF (retired) IAFF L-319
BSA Eagle Scout - Class of 1980
R.K.S. #1691; R.K.C.C. #CM83
N.R.A. Patron Life Member