TS-1635AX until recently was in use.  Upgraded to a 36-Bay NAS enclosure is the only reason for selling.

https://www.qnapworks.com/TS-1635AX.asp

Comes with upgrades:

QM2-20-244A https://eustore.qnap.com/qm2-2p-244a.html

2x 1TB BLUE SA510 2280 M.2 SSD

2x 1TB Blue SN570 SSD

3x Noctua PF Super Silent fans 

Get yourself the ultimate storage solution with this QNAP TS-1635ax NAS enclosure. With 19 bays and support for both HDD and SSD, you can store all your data with ease. This device also comes with features like cloud storage, hot plug support, hot swap, and remote access, making it a perfect fit for your personal or professional needs. In addition, this NAS enclosure has a built-in media server and supports multiple interfaces such as M.2, 10GBE, SATA III, and Gigabit Ethernet. With a write speed of 12x, you can transfer your data quickly and efficiently. Enjoy seamless access to your data with this versatile and reliable QNAP TS-1635ax NAS enclosure.