Yamaha FC4A - Piano Style Switching Sustain Pedal

Yes, the Yamaha FC4A - Piano Style Switching Sustain Pedal is compatible with the 'Sustain' port on the back of the Yamaha P-105 Digital Piano.

Yes, the Yamaha FC4A Piano Style Switching Sustain Pedal is compatible with the Yamaha DGX-670 88-Key Portable Digital Grand Piano with Speakers.

Yes, the Yamaha FC4A - Piano Style Switching Sustain Pedal is compatible with the Yamaha PSR-SX920.

The FC4a is a sustain pedal with only on/off control. The FC3A is a more advanced pedal that will, if your keyboard supports it, allow you to use the pedal for 'half-pedal' effects. In other words, you can partially depress the pedal and get less than a full pedaled sound. Half pedal effect is easier to achieve on a real, acoustic piano by pulling the damper felts partially off the strings. Someone mentioned in their comment that the FC3A is more hardy than the FC4: I own and have use a dozen of the FC4 in the past 25 years and though they do eventually wear out and have to be replaced, the FC3A is more complex and tends to have a slightly shorter lifespan. The first FC3A I ever owned, lasted about three years. It'll be good to keep in mind that I have thirty students stomping on it five hours a day, four days a week. The FC4 will suit most pianists just fine unless you want to play with or teach students the concept of half-pedal effects. (You will need to have an Yamaha FC3A PEDAL and also own a Yamaha instrument that supports half-pedaling. Different manufacturers use different polarities when designing their instruments so you have to make sure you get the polarity right. This can be done in various ways but is beyond the scope of this review.)

What the others have said, both metal and plastic but it's very sturdy. Hands down the best sustain pedal imho...and I've used many others over the years and they never last as long as the Yamaha. I used my original one for almost 20 years before it gave up!