Excellent topic. I moved this from the Mittenwald bass thread. It needs it's own space as it includes basses from all over.
Boy, have I seen some machines in my life. Some good and some not so good.
The gears you post are turn of the century German within the last 100-120 years or so.
The handles are Iron I think with laminated brass caps. That is the key with these, the brass caps over Iron. I have seen them used on various gears, on and off plates.
My Mittenwald has them in a heart shape handle, not a round shaped/oval button.
Please feel free to look thru the basses on my site and pull off the pics with these laminated brass capped gears. I have several basses with them including the gears formerly on my Gilkes but they were not original to the bass.
Ok, on the plates or no plates the English liked to do that from what I have seen as well as re-fit many Italian basses with them as well. Also, many Italian so called basses have since been identified as British. One point I want to make is that you should not solely identify a bass by it's gears. Even if they are 100% original to that scroll, how do you know for sure the scroll matches the bass?
On the 3-4 conversions, most basses I have seen do not have their original 3 gears with a 4th added. Some do, but many of them have had total replacements. Many basses especially Italian were made with less than desirable gears for modern use. Some may have been made with Cello type pegs or some other kind of tuning design in between.
My Panormo School bass has old English brass plates that seem original and the 2 of the 3 original Baker gears have been moved to cover the center hole of its 3-string days. The 4th gear is also a Baker but not 100% identical to the other 3 if you look close. Have a look yourself and tell me who's the new guy?
The Hawkes I just sold had 3 of its original Gears on the original plates, all moved to fit 4 gears with one similar gear added and the handles/buttons look to have been replaced on the Gears to fit the shorter pegbox.
Happy gear hunting.