These may also be something else (narrow compared to most RH examples) but are the basic design for the pre 1927 officers pattern tabs to be used with the field/service tunic of RH officers. In 1927 the waffenfarbe was introduced with branch colored tabs for service tunic wear.
I had seen lots of these tabs. I think yor example is a infantery officer tap with dirty, dark middle stripe. It can also be an faded transport stripe.
Laurence, here is a a Reichsheer Lt. with these universal collar tabs (silver cords) - note, the underlay of the shoulder boards is a different colour.
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