Part# ST2012 - Yella Terra Street Terra stud mount roller rocker set to suit Holden red motors, 149, 161, 179, 186 engines. Direct bolts on with no machining required. Economically priced, entry level rollers that have a strong vacuum die formed light weight arm designed for high performance street and budget race applications that do not have excessively high valve spring pressures. For use with hydraulic camshafts and 7/16 factory pressed in studs mounting, with a rocker arm ratio of 1.6 : 1 [studs not included]