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