Looks to be a tubeset assembled by Sauer's patent 70343 and also it appears to wear the "Crown" over Gothic F stamp of the Frankfurt an der Oder proofhouse. Water table doesn't look to be stepped(light weight variant?) but it wears their Nimrod trademark and the locks resemble a Nimrod. If so, behind each lock is a keeper to remove the mainspring.

Kind Regards,

Raimey
rse