This listing is for a pair of Optimus Pro 77 2-way crossovers. I have replaced the original 4.7uF electrolytic capacitors with Dayton Audio 4.7uF metalized polypropylene capacitors. In my opinion this upgrade improves the sound in the upper frequencies.

 These probably fit other Radio Shack/Optimus/RCA models. Please check your dimensions. These measure 2 1/4" by 2 5/8". The mounting hole opening measures 1 15/16" in diameter.