89 >syncro< GL - "red brick"

The van is new to me and i took delivery of the van without centre seat,
subsequently got the seat from the ex-wife, sans the 4? bolts that hold the
seat to the chasiss.  The guide holes are in place and are positioned OK.

Does anyone know what the thread and the presumably metric size is ?
before i camp out at the hardware store.

thanks. adrian