I've searched for info on this til my eyes are sore and all I come up with are DS-0 & DS-4.
Heeeeelp :-)

Here are the Billings pages from a 1931 Shadbolt & Boyd Catalog. I can't see a numbering pattern like that.

It isn't in the catalog, it's a special for a Draper Loom....
(DS - Draper Service wrench, I suspect)
There are at least 4, probably 5, you have (probably) the only flat one, there is an offset, and a T-handle, and something else I forget offhand...

Textile wrenches are really badly documented :(

DS-3 is more clearly a Textile wrench...

I read the part about it being for a draper loom, thought there would at least be info on it somewhere, but if they wern't well documented it may take some time. Thanks.