The SL600 Pinnacle Premium is Harmar's top stairlift. It is an indoor straight stairlift and has a sister model, the SL600S. Both stairlifts have the same features, but the SL600S has Harmar's wider signature seat and also better upholstery.

The standout feature of Harmar SL600 is its gear system. While most stair elevators use a rack-and-pinion system to move their carriages up and down the rails, the SL600 Pinnacle Premium employs a patented helical-worm gear drive system. This drive system has a number of advantages. First, it draws less power than conventional systems. With it, the SL600 can easily run twice the number of trips that conventional stairway lifts do. The new gear system can get up to 40 trips from the stairlift's battery when fully charged.

Another advantage of this gear system is that it requires no greases or special lubricants, so it is easy to maintain. In fact, Harmar has a 10-year warranty on the gear and a lifetime warranty on its track, as the helical-worm gear system is sturdy and requires little maintenance. However, the SL600 is the only stair elevator with this gear system. It is not even available in Harmar's other stair elevators, so you may have a hard time finding a technician or parts when it does need repairs.

Besides of its unique drive system, the Harmar SL600 Pinnacle Premium stairlift is very light and has a slim profile when folded. Even though it has a compact design, this stairlift can easily carry up to 350 pounds. It has a wide padded seat that rotates 90 degrees to allow you to get on and off easily. There is also a rocker control for moving the lift, wireless remote controls to call and send the lift up and down stairs, and safety sensors that stop the handicap stairlift when it encounters an obstruction.

The SL600 comes with useful optional features. A removable key lock is available for preventing unauthorized use of the stairlift. Other options include a foldable rail at the bottom of the stairs and an anodized bronze track. Homes with narrow stairs need the first option to make more room for foot traffic, while the second option is a cosmetic improvement on the standard track.

Harmar covers the SL600 with warranties on parts, batteries and its unique gear drive system. With its benefits and rarity, that system is the stairway's major strength and weakness.