The answer to your question can be found in DA PAM 670-1. Please see the reference below:
The following appurtenances may be worn on decorations, medals, ribbons, and other awards, when authorized by the
Oak Leaf Clusters.
(1) See AR 670–1 for wear policy.
(2) The silver oak leaf cluster is worn to the wearer’s right of a bronze oak leaf cluster and to the left of the “V” device. Oak leaf clusters, 5/16 inch in length, are worn on service ribbons, the suspension ribbon of miniature medals, and unit awards. Oak leaf clusters, 13/32 inch in length, are worn on the suspension ribbon of full-size medals. Oak leaf clusters 5/16 inch in length, joined together in series of two, three, and four clusters, are authorized for optional purchase and wear on service ribbons and unit award emblems. Personnel wear oak leaf clusters centered on the service ribbon and suspension ribbon, with the stems of the leaves pointing to the wearer’s right. If four oak leaf clusters are worn on the suspension ribbon on either full-size or miniature medals, the fourth one is placed above the middle one in the row of three. No more than four oak leaf clusters can be worn side-by-side on service ribbons.