The first model of Swiss PTT VW has been fitted with three different types of hubs and two baseplates
making four combinations :

1) ridged hubs, baseplate with dimple (rare)
2) ridged hubs, baseplate without dimple
3) spun concave hubs, baseplate without dimple
4) plastic hubs, baseplate without dimple

This confirms that the dimple has been deleted in 1959 - 1960 but not at the same time as the
reference number 181.