http://armypubs.army.mil/epubs/pdf/r600_8_22.pdf
Section II
Service Ribbon Accouterments
6–3. Oak Leaf Clusters
A bronze or silver twig of four oak leaves with three acorns on the stem, 13/32-inch long for the suspension ribbon,
and 5/16-inch long for the service ribbon bar and the unit award emblem is issued to denote award of second and
succeeding awards of decorations (other than the Air Medal), the Army Reserve Components Achievement Medal, and
unit awards. A silver Oak Leaf Cluster is worn instead of five bronze Oak Leaf Clusters. If the number of authorized
Oak Leaf Clusters exceeds four, a second ribbon is authorized for wear. When wearing the second ribbon, place it after
the first ribbon; the second ribbon counts as one award.
Wear no more than four Oak Leaf Clusters on each ribbon. If
the receipt of future awards reduces the number of Oak Leaf Clusters sufficiently (that is, a silver oak leaf cluster for
five awards), remove the second ribbon and place the appropriate number of devices on a single ribbon. Oak Leaf
Clusters are not issued for the Legion of Merit awarded in degrees to foreign nationals. Five-sixteenths inch Oak Leaf
Clusters joined together in series of 2, 3, and 4 clusters are authorized for optional purchase and wear on service
ribbons, and unit award emblems.
...
6–5. "V" device
The "V" device is a bronze block letter, V, 1/4-inch high with serifs at the top of the numbers. It is worn to denote
participation in acts of heroism involving conflict with an armed enemy. It was originally worn only on the suspension
and service ribbons of the Bronze Star Medal to denote an award made for heroism (valor). Effective 29 February
1964, the "V" device was also authorized for wear on the Air Medal and Army Commendation Medal for heroic acts or
valorous deeds not warranting awards of the Distinguished Flying Cross or the Bronze Star Medal with "V" device.
Effective 25 June 1963, the "V" device was authorized additionally for wear on the Joint Service Commendation Medal
when the award is for acts of valor (heroism) during participation in combat operations. In the case of multiple "V"
devices for the same award, only one "V" device is worn on the service ribbons.