Crown NAB reel adapters
The one's that came on my Crown SX824 decks work very well. I'll take a picture this weekend and post it.
Crown RTR decks were often found in the home stereo environment, but were used much more in a professional or commercial setting. The functionality of the NAB adapter hubs had to do several things. They had to hold the reel securely enough to prevent the loss of a reel during fast forward or rewinding operations as well as be quick and easy to use. You wouldn't want to spend much time fumbling with a reel adapter when changing reels if recording live, or during broadcast playback.
As the proud owner of several Pioneer RT series machines, I am very familiar with the hub adapter operation with the PP-220 and PP-220A adapters. Although they look nice and mine work well, it is more complex than with the Crown adapters.
The earlier style Crown reel adapter, shown here without a reel attached, is a simple to operate device. The center hub acts as the tensioner on a spring that can be tightened and loosened in order to increase or decrease the circumference of the spring.
As the center hub is "backed off", the tension on the spring results in a decrease of the spring circumference, which allows you to easily slip the reel onto the hub. After the reel is placed on the hub, you tighten the center hub which spreads the spring out and secures the reel.
There was a later style hub adapter that was even easier and quicker to use. It utilizes 3 spring-lock tabs to secure the reel.
You simply place the reel onto the hub in the correct position and press the hub down until you overcome the spring tension on the tabs and the reel drops into the correct position and is locked into place as the spring tabs return to their normal position, securing the reel.