Brand new, still-in-the-box D's Locks for TiLite ZR/ZRA, Spingery 12-spoke wheels. Retail value $870; asking $499. Free shipping or pick up in PHL.
The product info below is from the vendor:

Tired of brakes that don't work?

  • Positively lock wheels in place in any weather/tire condition
  • Single lever can be mounted almost anywhere for user convenience
  • Locks can be engaged and disengaged easily, even with limited hand control
  • Adds no width to most wheelchairs
  • Lightweight
  • Wheels can be removed and replaced with the locks engaged
  • Easy installation
  • Compatible with most everyday wheelchairs and wheelchair wheels

The D's Locks hub lock system is a revolutionary wheelchair brake substitute. These hub locks for manual wheelchairs take the place of traditional push-pull or scissor style brakes. The benefit of D's Locks is that they work independently of the tire by locking the wheel at the hub. Therefore tire types and air pressure no longer affect your ability to remain stationary. With one lever, both of your wheels can be locked securely in place simultaneously. D's Locks mount completely out of the way, so thumbs stay intact. Additionally, the brakes are no longer the widest part of the chair. In most cases they add little to no width. D's Locks can be installed in less than an hour. No special tools required!