From Hollywood Bike Racks:

The Hollywood Racks 2-Bike Add-On Kit For HR1450+HR1500 Racks - HR1475 bicycle holding features are the same as the Sport Rider SE2. Connects easily by simply sliding the add-on kit into the base unit, insert the attachment pin & clip, then tighten the lever. 

• Capacity: Two Bikes (Max. 50 lbs per bike)
• Fits HR1450, HR1450R, HRT220
• Includes patented “No-Wobble Hitch System" 
• Maximum bike wheelbase: 60” 
• Locking frame clamps
• Insert tube is 1-3/4" x 1-3/4"
• Space between bikes: 10” 
• Rack Weight: 37.50 lbs.

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