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.”

Body Size: 20, Backflow: w/o Backflow Function, Thread: Rc, Port Size: 1/4, Options: w/Set Nut, for Panel Mount, Set Pressure: 0.02 to 0.2 MPa Setting, Exhaust Mechanism: Relieving Type, Flow Direction: Left to Right, Knob: Downward, Pressure Units: Unit on Product Label: MPa, Pressure Gauge in SI Units: MPa

Body Size: 20, Backflow: w/o Backflow Function, Thread: Rc, Port Size: 02 (1/4), Options: H (w/Set Nut, for Panel Mount), Set Pressure: 1 (0.02 to 0.2 MPa Setting), Exhaust Mechanism: Relieving Type, Flow Direction: Left to Right, Knob: Downward, Pressure Units: Unit on Product Label: MPa, Pressure Gauge in SI Units: MPa

Body Size: 20, Backflow: w/o Backflow Function, Thread: Rc, Port Size: 02 (1/4), Options: H (w/Set Nut, for Panel Mount), Set Pressure: 0.05 to 0.85 MPa Setting, Exhaust Mechanism: N (Non-relieving Type), Flow Direction: Left to Right, Knob: Downward, Pressure Units: Unit on Product Label: MPa, Pressure Gauge in SI Units: MPa

Size: 1/8, Reverse Flow: Regulator, Standard, Thread: M Thread, Rc(PT), Port Size: 1/4, Accessory: Panel Mount w/Set Nut, Option 1: -, Option 2: -

This is a legacy product, and replaced byAR25-02H-BZ AR MASS PRO. REGULATOR, MODULAR. AIRLINE EQUIPMENT. AR MASS PRO 1/4 MODULAR (PT). .55878 lb. DA.

This is a legacy product, and replaced byAW40-02H-B

This is a legacy product, and replaced byAW20-02H-C-B, FILTER REGULATOR, MODULAR, AIRLINE EQUIPMENT, AW MASS PRO, DA, AW MASS PRO 1/4 MODULAR (PT), 0.74957 lb

This is a legacy product, and replaced byAW20-02H-C-B

This is a legacy product, and replaced byAW20-02H-7C-10-B, FILTER REGULATOR MODULAR *LQA, AIRLINE EQUIPMENT, AW FILTER/REGULATOR, DA, AW 1/4INCH MODULAR (PT), .95343 lb

This is a legacy product, and replaced byAW30-02H-B

This is a legacy product, and replaced byAR40-02H-B, REGULATOR, MODULAR *LQA, AIRLINE EQUIPMENT, AR REGULATOR, DA, AR 1/4INCH MODULAR (PT), 1.94649 lb, Regulator Series ARPages 346 through to 355ModelPort sizeOptionsRegulator Series ARPages 346 through to 355AR401/4, 3/8, 1/2BracketSquare embedded type pressure gauge (except the AR10)Round type pressure gauge Digital pressure

This is a legacy product, and replaced byARP30-02H

This is a legacy product, and replaced byAR20-02H-B, REGULATOR, MODULAR, AIRLINE EQUIPMENT, AR MASS PRO, DA, AR MASS PRO 1/4 MODULAR (PT), 0.48272 lb

This is a legacy product, and replaced byAR20-02H-B, REGULATOR (SHIKOMI ORDER ONLY), AIRLINE EQUIPMENT, AR REGULATOR, DA, AR 1/4INCH MODULAR (PT), .59403 lb, Regulator Series ARPages 346 through to 355ModelPort sizeOptionsRegulator Series ARPages 346 through to 355AR201/8, 1/4BracketSquare embedded type pressure gauge (except the AR10)Round type pressure gauge Digital pressure

This is a legacy product, and replaced byAR20-02H-R-B, REGULATOR, MODULAR *LQA, AIRLINE EQUIPMENT, AR REGULATOR, DA, AR 1/4INCH MODULAR (PT), .59524 lb, Regulator Series ARPages 346 through to 355ModelPort sizeOptionsRegulator Series ARPages 346 through to 355AR201/8, 1/4BracketSquare embedded type pressure gauge (except the AR10)Round type pressure gauge Digital pressure

This is a legacy product, and replaced byAR20K-02H-B, http://smcpneumatics.com/assets/images/pdf/ar.pdf

This is a legacy product, and replaced byAR25K-02H-B, REGULATOR, MODULAR, AIRLINE EQUIPMENT, AR MASS PRO, DA, AR MASS PRO 1/4 MODULAR (PT), .56918 lb

This is a legacy product, and replaced byAR25-02H-B

This is a legacy product, and replaced byAR30-02H-B, REGULATOR, MODULAR *LQA, AIRLINE EQUIPMENT, AR REGULATOR, DA, AR 1/4INCH MODULAR (PT), .09038 lb, Regulator Series ARPages 346 through to 355ModelPort sizeOptionsRegulator Series ARPages 346 through to 355AR301/4, 3/8BracketSquare embedded type pressure gauge (except the AR10)Round type pressure gauge Digital pressure