Mounts with 2 M4 bolts. I had a leveling tube laying around from an Ikea shelf kit, but can purchase here:
https://www.amazon.com/Pieces-Cylindrical-Horizontal-9-5x40mm-Measuring/dp/B0BVQ7HWVJ/ref=sr_1_1?crid=30GZRW129MPS6&dib=eyJ2IjoiMSJ9.HiWmDTbfyhpg-yyOajcMIZrLHnZW1JVBN47X1MhyVlh9L5UF_8cne6Usdnu8d40uT_o1LIPwR3kUbPmUFqH3Fzx9H3lpAp7MkiT5o4OMMFUPOW-5zgjKsiXrr13n437FQWiiBI18mKFnz46RV-z33cRTL_yBYp0V2Xm1zKKOXMLPnpGoD439ra55NKCzJyRohpw5b2oVT2hKLgWDk-D7LWGjLxgQQbNNHJrVgYuKUqq4oys7tIY8DKgEDb4eYfkj-jKVVS5DpzoSGuvZVjkUa0KTM2DCsHZsJT_6EIax8r4.-F4Dlk70y1KVyporhMAVP76bXHz_tsOufGvDD-vf5Mk&dib_tag=se&keywords=level+tube&qid=1726026372&sprefix=level+tub%2Caps%2C143&sr=8-1
The author remixed this model.
Accessory to the EQ mount to aid leveling and alignment.