Various designs I've needed over the years. Some is openscad, for 3d printing, some are just vectors for laser cutting.
We needed to adjust the height of some plates. This fits between the wells of a 6, 12, or 24 well plate, and functions as a "nut" into which a stainless bolt can be screwed, providing "legs" for the plate.
This should be cut into 5mm thick acrylic, and forms a rack to hold 12 10mL syringes, with reusable filters attached. We used this while sampling epiphytic bacteria from plants in the field.