Here is a brief outline MauserBill wrote in 2007:
The gew98 has a roughly 15.625" long rod. Roughly as they can vary easily by as much as 3/32 OAL. As well many have been repaired when the threaded end got snapped off or worn out.
Anyhow if the cleaning rod does not have a two digit serial on the tulip and or a fraktur proof on the stem below the tulip , it's not a gew98 issue rod. No exceptions.
The rods made for the brazilian pre WW1 contract 1908 rifles have the exact same rod as the gew98 , but no two digit serial nor fraktur proof. These brazilian rods will usually have a kind of curved looking letter 'B' stamped on the stem below the tulip. I have seen some fellows buff this mark off to hide the origin of the rod when put with a gew98 , but no serial and or proof - no good.
I do have some 70 or 80 original gew98 rods on hand . I trade rod for rod depending on what serial you seek. If you need rod #31 for example and I have it , just send me an unboinkered serialed gew98 in swap for it.
