Before the regulations of 1915, this was the ONLY style of ribbon bar under Prussian and Reichs regulations:
Flat overlapped ribbons in a truncated pyramid shape of roughly the same size as would be found on a full size group of parade mounted medals.
Officers generally wore this style without any suspension hooks on the back, because this style was worn ONLY as a ribbon bar. Enlisted ranks wore the same style, but with hooks on back so that they could change from ribbon bars to medal bars.
Illustrated here are a variety dating from the 1890s to the 1930s of sizes worn on different forms of dress:
TOP: circa 1897 about half normal size, as worn by a civilian with miniature medals or as a ribbon bar
SECOND: a small size with 15mm ribbons first actually worn before the war on naval officers' "monkey jacket" mess dress, but here as worn during WW1 on a reefer jacket. This size is almost always naval, and persisted in wear into the Second World War among very old fashioned naval officers.
THIRD: another smaller version, almost full sized, worn on some sort of civilian clothes in the 1930s, by which time this was a VERY outdated style indeed.
FOURTH: this is actually a Bavarian officer's Prussian (!!!) style bar from the first two years of the First World War. bavarians usually wore the "South German" style-- see that section.
For additional types see the scans following each style section.
1st, 2nd, 3rd courtesy of David S