O and O27 track dimensions

I never can seem to find O gauge track dimensions and other key information about O and O27 track when I need to find them. So I’m finding them one last time and collecting them here. Maybe someone else can use the information.

O and O27 track gauge

The major differences between O and O27 track are the size of the ties and the size of the smallest curve.

O gauge is 1.25 inches from inside rail to inside rail. O27 is the same. The difference between O and O27 is the height of the track and the diameter of the standard circle.

O and O27 track dimensions

O gauge track stands 11/16″ high from the bottom of the tie to the top of the rail. O27 track stands 7/16″ high, also measured from the bottom of the tie to the top of the rail. Note the difference is 1/4 inch.

Standard O27 straight track sections are 8.875 inches long. O straight sections are 10 inches long. Longer sections of each type are available. Typically they are around 3 feet in length but the precise length can and does vary.

Curved O pieces make a circle about 31 inches in diameter. The curved pieces are 10 7/8 inches in length. O31 track uses 8 track sections per circle, with one piece making a 45-degree turn. Curved O27 pieces make a circle about 27 inches in diameter. The curved pieces are 9.5 inches in length. O27 track also uses 8 track sections per circle, with each piece making a 45-degree turn.

Wider curves

Wide-diameter O42 track uses 12 track sections per circle, with each piece making a 30-degree turn. O54 and O72 track uses 16 track pieces per circle, with each piece making a 22.5-degree turn.

Marx made a 34-inch curve during the postwar era. It made a 45-degree turn with 8 pieces per circle.

Mixing curves

O54 and O72 wide-diameter track uses 16 track sections per circle, so you can use them to transition into a sharper curve for smoother running. Instead of going around a corner with two curved pieces, use three, with the wider-diameter pieces at the start and end. By shortening up the straight lengths, you can make these transitions without having to increase the size of your table. The transitions give you most of the benefit of the wider diameter track when you normally wouldn’t have room for the wider curves.

O and O27 track pins

O gauge track pins are 7/64 inch. O27 track pins are 3/32 inch. 7/64 inch is about equivalent to 10 gauge wire. 3/32 inches is about equivalent to 12 gauge wire.

O and O27 track tie dimensions

O gauge track ties measure 2 1/4 inches long by 19/32 inch wide. O27 track ties measure 2 inches long by 1/2 inch wide.

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