Abstract: Adapters are provided for opposed cradle heads of a shaker arm for mounting a plurality of containers of different sizes. The cradle heads are provided with arcuate grooves and flanges in opposition to one another and the adapters are provided with bases having complementary arcuate grooves and flanges. With the adapters mounted on the cradle heads with interfitting grooves and flanges, multiple containers are disposed in container end supports in the adapters whereby oscillatory movement of a shaker arm oscillates the cradle heads, adapters and containers.