Quad monitor arm. Is set up in a triple monitor with a 4th monitor on top. Can accommodate up to 24inch monitors. Triple arm is by a company called Mool (https://www.amazon.co.uk/MOOL-Professional-Bracket-Capacity-Mechanism/dp/B00UBOLSME) and I’ve modified with a longer central arm and 4th monitor bracket from Duronic. £50 + P&P Or can collect from Benfleet, Essex.