“Using specially manufactured 16.5 mm (0.65 in) gauge track, scaled at 7 mm to the foot (with appropriately spaced, larger Railroad Tie underneath – United States O scale rolling stock (1:48), it becomes a narrow-gauge track of 2 ft 6 in (762 mm), and is referred to as “On 2½” (or On30, as in 30 inches).” ^{1}Wikipedia – O scaleThis is based on HO track. If you run the numbers, that 16.5 mm (0.65 in) gauge track actually comes out to a 31.18 in (792 mm). Since there was a real world 30 in gauge track we simply call this On30 .. rather than On31. |

## NMRA S-7 ClearancesThis is from the NMRA S-7 Clearances It states that “ |

## ON30**A**– This is from the centerline to the outside of the body so represents half the width. The body width then is 2 x**A**or 3″. Full-size this is 144″/12′.- For On3 this is
**A**= gauge x 2 (36″ x 2 = 72″). Car width would be twice this or gauge x 4 = 144″ - Since there is a direct correlation between car width and gauge and stability I will modify the dimensions for On30 using the ratio for On3 above.
- If we used those same ratios for On30 this would be
**A**= gauge x 2.4 (30″ x 2.4 = 72″). Car width would be twice this or gauge x 4.8 or 144″. If we keep the same multiplier we used for 3 ft narrow gauge (gauge x 4) then we would come up with**A**= 30″ x 2 = 60″. Car width would be twice this or 30″ x 4 = 120″. Therefore,**A**= 1.25 in / 31.75 mm and 2 x**A**is 2.5″. I rounded up those last numbers so that**A**= 32 mm or 2 x**A**= 64 mm for car width. Again .. I did this to keep the correlation between car width and track gauge the same as we have for On3. - I took 12 mm from the center which made
**P**and**G**29 mm. I kept the 19mm for**B**and changed the angle down to**D**.
Will this work with Bachmann On30? Have not idea – they may need to use the On3 gauge – will check at some point. |

## On30 GaugeThe last thing to consider is the locator tab that fits between the rails. -
- Width : 16.5 mm (0.65 in) gauge track – since I need the tab to fit ‘easily’ I am reducing the width by .1mm to 16.4 mm (0.646 in) – for now at least. I may need to modify that after printing a gauge.
- Depth: Looking at the Flange Clearance chart on Brunel Hobbies’ Flex Track & Rail Facts page we see that a 0.035″ depth will clear the spike on Code 55 rail.
I cranked off this gauge .. call it version 1. |