The 20-ton Ust (18.1 metric ton) lifting capacity National Crane 600H Series Boom Truck product lineup originally consisted of six models with boom options available from 38 ft (11, 58 m) to 90 ft. (27, 42 m). 

Series Features:

• Multiple outrigger positions
• Standard RCL System
• Internal anti-two block wiring
• Rear or tractor mount options
• Three and four-section boom options
• Mentor LMI system
• Easy Glide wear pads
• Proportional boom extension
• High-performance planetary winch

National Crane 649H – Equipped with a 16 ft - 49 ft  (4.88 m -15 m) four-section boom. The maximum tip height is 59 ft (17.98 m).

National Crane 660H – Equipped with a 24 ft - 60 ft (7.32 m - 18.3 m) three-section boom. The maximum tip height is 70 ft. 21, 3 m. 

National Crane 680H / National Crane 680H-TM (Tractor Mount) – Equipped with a 24 ft - 80 ft (7.32 m - 24.38 m) four-section boom. The maximum tip height is 90 ft (27.44 m).

National Crane 690H – Equipped with a 27 ft - 90 ft (8.23 m - 27.43 m) four-section boom. Previously this model came equipped with a Model 6FJ45M 25 ft - 45 ft (7.62 m - 13.72 m) two-section jib for a maximum tip height of 144 ft (43.95 m). 

Below are models no longer officially part of the Series lineup. 

National Crane 638H – Equipped with a 16 ft - 38 ft (4.88 m - 11.58 m)  three-section boom. Maximum tip height is 48 ft (14, 63 m).

National Crane 671H – Equipped with a 27 ft - 71 ft (8.23 m - 21.64 m)  three-section boom. This model can be equipped with a Model 6FJ45M 25 ft - 45 ft (7.62 m - 13.72 m) two-section jib for a maximum tip height of 125 ft (38.25 m).

National Crane 684H-TM (Tractor Mount) Equipped with a six-section 19' - 84' (7.32 - 24.38 m) telescopic main boom for a maximum tip height is 94' (28.6 m).