F03.

Refer to the AR-A/AR-B/AR-D series catalog excerpt, which has been reproduced below.
The part number of the standard AR20 to AR60 round type pressure gauge is “G36-10-01,” or “G46-10-01”(for the R thread type).
For example, the part number of the AR30-03BG-A pressure gauge is “G36-10-01.”

Refer to the AR-A/AR-B/AR-D series catalog excerpt, which has been reproduced below.
The part numbers of standard AR20 to AR60 round type pressure gauges are “G36-10-01” and “G46-10-01”(for the R thread type).
For example, the part number of the AR30-03BG-A pressure gauge is “G36-10-01.”

AR10-A: Rc1/16
AR20-A to AR40-A, AR20(K)-B to AR60(K)-B, and AR20(K)-D to AR40(K)-D: Rc1/8
Old AR10: Rc1/16
Old AR20(K) to AR30(K): Rc1/8
Old AR40(K) to AR60(K): Rc1/4
Old AR1000: Rc1/16
Old AR2000 to AR3000: Rc1/8
Old AR4000 to AR6000: Rc1/4

AR10-A: Rc1/16
AR20-A to AR40-A, AR20(K)-B to AR60(K)-B, and AR20(K)-D to AR40(K)-D: Rc1/8
Old AR10: Rc1/16
Old AR20(K) to AR30(K): Rc1/8
Old AR40(K) to AR60(K): Rc1/4
Old AR1000: Rc1/16
Old AR2000 to AR3000: Rc1/8
Old AR4000 to AR6000: Rc1/4

Options include a mounting bracket and set nuts for panel mounting, and a pressure gauge.

This is a legacy product, and replaced by25A-AR30-02B-D REGULATOR, MODULAR F.R.L.. REGULATOR. 360 lb. FVD.

Body Size: 30, Thread: Rc (Rc: for Sizes 20, 25, 30, 40; M5: for Size 10), Port Size: 02 (1/4), Option: H (Set Nut for Panel Fitting), Semi-Standard: 1 (0.02 to 0.2MPa Setting)

Body Size: 30, Thread: F (G), Port Size: 02 (1/4), Option: H (Set Nut for Panel Fitting), Semi-Standard: 1 (0.02 to 0.2MPa Setting)

Body Size: 30, Thread: Rc (Rc: for Sizes 20, 25, 30, 40; M5: for Size 10), Port Size: 02 (1/4), Option: GH (G + H), Semi-Standard: 1 (0.02 to 0.2MPa Setting)

Body Size: 30, Thread: F (G), Port Size: 02 (1/4), Option: w/o Mounting Option, w/o Pressure Gauge, Semi-Standard: 1 (0.02 to 0.2MPa Setting)

Body Size: 30, Thread: Rc (Rc: for Sizes 20, 25, 30, 40; M5: for Size 10), Port Size: 03 (3/8), Option: GH (G + H), Semi-Standard: 1 (0.02 to 0.2MPa Setting)

Body Size: 30, Thread: F (G), Port Size: 02 (1/4), Option: G (For Sizes 20, 25, 30, 40: Round Pressure Gauge w/Limit Indicator; For Size 10 Round Pressure Gauge w/o Limit Indicator), Semi-Standard: 1 (0.02 to 0.2MPa Setting)

Body Size: 30, Thread: F (G), Port Size: 03 (3/8), Option: M (Round Pressure Gauge w/ Color Zone), Semi-Standard: 1 (0.02 to 0.2MPa Setting)

Body Size: 30, Thread: Rc (Rc: for Sizes 20, 25, 30, 40; M5: for Size 10), Port Size: 02 (1/4), Option: w/o Mounting Option, w/o Pressure Gauge, Semi-Standard: 1 (0.02 to 0.2MPa Setting)

Body Size: 30, Thread: F (G), Port Size: 03 (3/8), Option: G (For Sizes 20, 25, 30, 40: Round Pressure Gauge w/Limit Indicator; For Size 10 Round Pressure Gauge w/o Limit Indicator), Semi-Standard: 1 (0.02 to 0.2MPa Setting)

Body Size: 30, Thread: F (G), Port Size: 03 (3/8), Option: BG (B + G), Semi-Standard: 1 (0.02 to 0.2MPa Setting)

Body Size: 30, Thread: Rc (Rc: for Sizes 20, 25, 30, 40; M5: for Size 10), Port Size: 02 (1/4), Option: G (For Sizes 20, 25, 30, 40: Round Pressure Gauge w/Limit Indicator; For Size 10 Round Pressure Gauge w/o Limit Indicator), Semi-Standard: 1 (0.02 to 0.2MPa Setting)

Body Size: 30, Thread: Rc (Rc: for Sizes 20, 25, 30, 40; M5: for Size 10), Port Size: 1/4, Option: G + H, Semi-Standard: 0.02 to 0.2MPa Setting

Body Size: 30, Thread: Rc (Rc: for Sizes 20, 25, 30, 40; M5: for Size 10), Port Size: 1/4, Option: H + M, Semi-Standard: 0.02 to 0.2MPa Setting