G Thread is Parallel (straight) threads (BSPP - British Standard Pipe Parallel), which have a constant diameter. The NPT thread is slightly tapered, while the G connection is straight. No Washer Needed.

G Thread (Metric BSPP) Male to NPT Thread Female Pipe Fitting Adapter - Lead-Free Adapter

1" x 1" (1 Piece) (49 En stock)
1" x 1" (2 Pieces) (12 En stock)
1" x 1" (4 Pieces) (2 En stock)
1/2" x 1/2" (1 Piece) (146 En stock)
1/2" x 1/2" (2 Pieces) (4 En stock)
1/2" x 1/2" (4 Pieces) (10 En stock)
1/2" x 3/4" (1 Piece) (38 En stock)
1/2" x 3/4" (2 Pieces) (8 En stock)
1/2" x 3/4" (4 Pieces) (10 En stock)
3/4" x 1/2" (1 Piece) (12 En stock)
3/4" x 1/2" (2 Pieces) (10 En stock)
3/4" x 1/2" (4 Pieces) (5 En stock)
1/4" x 1/4" (1 Piece) (248 En stock)
1/4" x 1/4" (2 Pieces) (13 En stock)
1/4" x 1/4" (4 Pieces) (9 En stock)
1 1/2" x 1 1/2" (1 Piece) (17 En stock)
1 1/2" x 1 1/2" (2 Pieces) (6 En stock)
1 1/2" x 1 1/2" (4 Pieces) (48 En stock)
2" x 2" (1 Piece) (6 En stock)
2" x 2" (2 Pieces) (50 En stock)
2" x 2" (4 Pieces) (49 En stock)
3" x 3" (1 Piece) (5 En stock)
3" x 3" (2 Pieces) (50 En stock)
3" x 3" (4 Pieces) (50 En stock)
3/8" x 3/8" (1 Piece) (0 En stock)
3/8" x 3/8" (2 Pieces) (10 En stock)
3/8" x 3/8" (4 Pieces) (11 En stock)
3/4" x 3/4" (1 Piece) (96 En stock)
3/4" x 3/4" (2 Pieces) (6 En stock)
3/4" x 3/4" (4 Pieces) (12 En stock)