A small ball and matching socket that allows you to position parts at any angle.
Their small size and ability to build organic shapes makes them especially popular when building realistic models of nature.
One challenge people sometimes face is that the connection is only so strong, which is why they are best suited to relatively small models or smaller details on larger models.
228901×2 Plate w/ Towball, End
31701×2 Plate w/ Towball, Both Ends
144191×2 Plate w/ Towball & Socket, Ends
144171×2 Plate w/ Towball, Side
31841×4 Plate w/ Towball, Side
154562×2 Plate w/ Towball, Side
144181×2 Plate w/ Towball Socket, End
147041×2 Plate w/ Towball Socket, Side
982631×4 Plate w/ Towball Socket, Side
630822×2 Plate w/ Towball Socket
22484Bar 1L w/ Towball
2736Technic Axle w/ Towball
66906Technic Pin w/ Towball
804773L Towball, Bar w/ Pin 
30395Hook w/ Towball
25082×4 Wedge w/ Towball