Ribe and Spline bits

[GabrielKnight]

I've been looking at a great socket set, but it also includes some 'ribe' and some 'spline' bits.

On which sort of items are these threads found?

How common are they?

 

[xerxes]

Some automotive fasteners have ribe or spline heads (not threads). Commoner on Italian vehicles?

I once needed a spline bit for a (now long-departed) Volvo; have never needed any since.

 

[crazycanuck]

in north america most car head lights and tail lights use ribbed drivers