This product is either discontinued or we cannot get that from suppliers.
Qnap SP-HS-TRAY HDD Tray, For HS Series NAS Accessories, Mounting Tray, Device Hard Disk Drive, Compatibility QNAP HS-210 Silent NAS.
The HS Series HDD Tray from Qnap is used to mount 2.5" and 3.5" HDDs. It is compatible with HS-210 NAS of Home & SOHO series.