The rails should have a bracket into which a 13mm bolt (if I remember correctly)  will thread. When the seat is out, the rail covers have a bolt that threads into those brackets to secure the covers. 

In point of fact, those bolte are really only to secure the middle seat from sliding left and right, as the rails are what keep it from moving backwards and forwards. I don’t remember if there are 2 bolts or 4 bolts for the single seat. A double seat should have 4 (2 on each rail). A double seat is so tight to the cabinet on one side and the door on the other, that it really won’t slide left/right when the door is closed. But for crash safety (in the event of a rollover) it should still be bolted down. 

> On Sep 28, 2016, at 10:44 PM, Eric Caron <ecaron1@COMCAST.NET> wrote:
> 
> Hi listers,
> 
>        I have a middle seat for my 85 Westfalia that slide on the rails.  It came with no hardware when gifted to me. 
> 
> What is the correct way to secure the seat once it has ben slid onto the rails? 
> 
> Eric Caron 
> 85 GL Auto Westfalia