The smallest design of the Shay, referred to as Class A, was available in different sizes between 6 and 24 tons. One of the oldest engines had the serial number 131 and was built in 1885 for the logging company T.L. Hackney in Texas. It had a service weight of nine short tons and was built for a gauge of 36 inches. The boiler was still arranged vertically and instead of a driver's cab there was only a large roof without side panels. After its service life at T.L. Hackney it came to the Rusk Iron Works, also in Texas. 

A few years after the construction of the first engines, the design of the Shay locomotives changed from the vertical boiler to a classic, horizontal boiler barrel with clearly visible steam and sand domes. One of these nine-ton-class models was procured by the Gilpin Tramway in 1887 for its 15.5-mile route in Gilpin County near Denver, with a two-foot gauge. It had the factory number 181 and was given the number 1 and the name “Gilpin” by its owner. Four more Shays followed in the years up to 1902 with 12, 15, 17 and 18 tons. The first two were sold in 1905, the others remained in service until the line was closed in 1917.

One of the standard models of the Shay built in larger numbers was the class B in the version with a service weight of about 50 short tons. Like all B, C and D class models, they had three cylinders. Some of the B-50-2 model locomotives already had a boiler pressure of 220 psi, while most others were still operated at 200 psi. In the meantime, the gear parts on the right side of the locomotives were covered to protect them from dirt while working in the forest. Curb weight was 85,800 pounds for early examples and approached 99,000 pounds for locomotives from the mid-20's.

The Lake Independence Lumber Company in Michigan operated a total of five B-50-2s in addition to one B-42-2. Two of these had been built in 1910 and 1911 for other logging companies and came to this company later. Two more had been built directly for the Lake Independence Lumber Co. in 1914 and 1925 and an identical 1923 example had been purchased from Lima stocks. All five were resold in the 1920s, four of them to the Brunswick Lumber Company.

The heaviest Shays belonged to class C and had three two-axle bogies with a service weight of 160 short tons. Likewise, the class D with four bogies up to 150 short tons was offered, which could score with slightly lower power figures with larger reserves and a higher adhesive weight. A common model with three bogies in the 150 ton weight class is presented here. In terms of the number of cylinders, it did not differ from the smallest B-class models, but the cylinders were significantly larger with a diameter of 17 inches and a piston stroke of 18 inches.

No. 6 in front of a freight train

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The Western Maryland Railway already had one C-70-3 and one D-150-4 type and procured another C-150-3 in 1945. The special thing about this locomotive is that it was the last of about 2,770 Shays built. After the Western Maryland introduced diesel locomotives on main lines beginning in 1949, the number 6 was retired in September 1950 after only five years of service. In 1953 it came to the Baltimore & Ohio Transportation Museum and from there it has been on loan to the state of West Virginia since 1980 for use on the Cass Scenic Railroad. It is considered the largest operational Shay today.

While the first Class A Climax locomotives still had a vertical boiler and vertical cylinders, the majority of the later classes A, B and C got a horizontal boiler and laterally mounted, horizontal or inclined cylinders. The machine last run as Hillcrest Lumber Company No. 9 was a two bogie class B example. Classified in the 50-tons category, it was actually quite a bit lighter. It used oil as fuel. The maximum train loads of locomotives in this class were over 2,000 tons on level ground and 130 tons on a six percent incline.

The locomotive was built in 1915 for the M.D. Olds Lumber Company in Michigan, but turned out to be too light for their purpose and was sold to Vancouver in Canada in 1917. There it was involved in the collection of wood for aircraft construction, but after the end of the war the demand collapsed and led to another sale. After another change of ownership, it finally came to the Hillcrest Lumber Company, where it served from 1936 to 1968. It was then used a few more times for special trips and today it is on display at the British Columbia Forest Discovery Center in Duncan.

The 55-mile-long San Joaquin & Eastern was built in Fresno County, California in 1912 to serve the Big Creek hydroelectric dam site. Since it was sometimes described as the most crooked railway line in the world, steam locomotives with bogies were used on the mountainous sections. After five Shays from 1912, six more Climax were purchased between 1916 and 1923.

The first five of these were of the three-truck C class with 70 tons. Like many railroads in the region, they were fired by oil. When the unprofitable line closed in 1933, No. 108 shown was shipped overseas. The sixth Climax with number 110 from 1923 was of the B class with 45 tons.

Geared locomotives could also be exported to other countries if their use was appropriate due to local conditions. One customer was the Taupo Totara Timber Company, TTT for short, which was founded in 1903 in Mokai on the North Island of New Zealand. They laid a 50-mile cape gauge main line from the NZR network to Mokai, and from there fanned out sidings into the forest. Due to the connection to the national route network, the main line was built with great effort, while the sidings were simply laid in the forest, as is usual for logging railways. Therefore, locomotives were needed that allowed safe operation on rough, winding and mountainous routes, but were also fast enough for the main line.

Of the ten locomotives that TTT purchased between 1903 and 1937, four were of the Heisler design. The last of these was number 9 shown, which had been delivered in 1921. It belonged to the type 32-8-30, which indicated a service weight of 32 short tons, eight powered wheels and a wheel diameter of 30 inches. It had a boiler pressure of just 160 psi, compared to the 180 or 200 psi of the larger variants.

The Heisler locomotives were used together with conventional and geared locomotives from different manufacturers. A point of interest on their route was the bridge over the Waikato at Ongaroto, which at the time had the longest span in the southern hemisphere. Unfortunately, this bridge in particular could not benefit from an urgently needed renovation after the sawmill in Mokai burned down in 1928 and the TTT therefore lacked the financial means. It is said that the condition of the bridge soon became so bad that the crew and passengers jumped off the train just before the bridge. This then crawled across the bridge without a driver while the people waded through the river and got back on at the other side. The company finally closed its doors in 1944 and part of the main line was then operated by the state railway.

The largest type among the Heisler locomotives was the 90-12-40. This meant a service weight of 90 short tons, twelve wheels and a wheel diameter of 40 inches. With this, an additional tender was stored on a third, two-axle bogie, which was also connected to the drive shaft. Although Charles L. Heisler's patent originally included four-cylinder locomotives, the largest locomotives were also built with two cylinders and an increased boiler pressure of 200psi. The maximum train weight was around 600 tons on a gradient of two percent and 225 tons at five percent. In theory, up to 4,000 tons were possible on the flat, but these geared locomotives were not intended for the flat country.

A surviving example of the large design is the standard gauge number 6 of the Cass Scenic Railroad. The latter operates an eleven mile long, very hilly line in the Allegheny Mountains in West Virginia, which was built in 1901. On the Cass Scenic Railroad, the Heisler, built in 1929, is the only one of its kind, while the other engines consist of a Climax and otherwise only Shays. Today, like the rest of the fleet, it is still owned by the state of West Virginia, but is now used in Durbin by the operating company Durbin and Greenbrier Valley Railroad. The locomotive was originally built for the Meadow River Lumber Company, which at the time operated one of the largest sawmills in the world.