These are a really nice upgrade or replacement part for your car and are a perfect blue colour match to Tamiya hop-ups!
They will fit lots of different Tamiya (and other) chassis, and are commonly used in 1/10 touring cars. I've picked up a set to replace the ball connectors on my TRF415MSXX - which actually takes 3 different types of ball connector, so make sure that you get the right part! These are the ones that go on the bottom arms - the ones used to connect the bottom of the suspension on the TRF415MSXX.
I like to wipe a very very tiny amount of Tamiya Cera-grease HG onto the ball before I push on the connector. It makes it easier to snap the connector on and keeps everything running really smoothly on most ball connections I tend not to do this on the bottom suspension connectors as they can clog up a little with dust and dirt - best to leave these as clean as possible as the grease may attract dirt.
They are very durable and if you look after your chassis and clean it regularly they will last a long time. You should always replace ball connectors when they show signs of wear or any pits and marks in them.