Torsion arm tube bush.
These spring plate bushes ensure that the rear suspension spring plate is able to rotate from a fixed pivot position. If your rear suspension is sagging it could be a sign that the bushes have perished or collapsed over time and need replacing. 
When re-indexing the rear suspension springplates we would always recommend taking the opportunity to replace these bushes as they have often never been replaced. 
This is the 'knobbly' style springplate bush, and is sided and used in conjunction with the corresponding opposite sided knobbly bush 311-511-245 and depending on the application also used with a pair of the smooth bushes 111-511-245/E

Manufactured by Vibrasil an OE supplier to VW

Vehicle and position fitments:
Beetle 60-68 with manual transmission - right outer and left inner
Beetle 68-79 with auto transmission – left inner
Beetle 69-79 with manual transmission – left inner
Karmann Ghia 60-68 with manual transmission - right outer and left inner
Karmann Ghia 68-79 with auto transmission – left inner
Karmann Ghia 69-79 with manual transmission – left inner
Type 3 62-73 right inner

Porsche 924 76-79 left inner