Each bar designates 5 years of service. If service was during war year a red background was added for Infantry & Cavalry or blue background for Artillery. Service stripes would be uncommon in early war images when only Regular Army soldiers would qualify for them. With the reenlistment of veteran volunteers, service stripes were seen in late war images among the volunteers, who would have had less than five years service in a war that did not last that long. This was authorized by General Orders 191 of June 25, 1863 as a distinction for those whose re-enlistments as veteran volunteers were badly needed. Priced per set of two, one for each sleeve.
U.S. Army Uniform Regulations, 1861: 1558. To indicate service–all non-commissioned officers, musicians and privates, who have served faithfully for the term of five years, will wear, as a mark of distinction, upon both sleeves of the uniform coat, below the elbow, a diagonal chevron, one-half an inch wide, extending from seam to seam, the front end nearest the cuff, and one-half an inch above the point of the cuff, to be of the same color as the edging on the coat. In like manner, an additional half chevron, above and parallel to the first, for every subsequent five years of faithful service; distance between each chevron one-fourth of an inch. Service in war will be indicated by a light or sky blue stripe on each side of the chevron for Artillery, and a red stripe for all other corps, the stripe to be one-eighth of an inch wide.