G-thread (from Gas or Gewinde) is a 55 degree parallel pipe thread. These can have male or female thread and o-rings can be used for low pressure lines under static load.
G-threads are NOT compatible with NPS, nor are they compatible with any tapered thread such as NPT or BSPT. The angle, shape, and thread-pitch of the threads are different, and attempting to use or force the use of these threads can damage the fitting, requiring replacement.
According to the current G-thread standard, the specs are identical to BSPP (British Standard Pipe Parallel) and can be used interchangeably. If, for example, you have a G1/8 fitting, you can use a 1/8″ BSPP fitting in its place.
You may encounter G-thread fittings or threaded holes on some European vehicles.
BSPP to AN adapter fittings are available on our website under the BSP Adapters product category.
