I designed these to hold a 3mm thick by 200mm wide glass/plexi shelf at a particular height of 130mm, to accommodate my giant Lego minifigs and other models. I also added a small front and rear lip to stop the glass from sliding forward/backward accidentally.
The end holders are 15mm wide and the middle holder is 10mm wide. The glass/plexi shelf will stand 130mm high. Each support was made in two pieces due to the size restriction of my original printer bed at the time.
Simply print the 15mm Part 1 and Part 2 - one for each end support you need (usually 2 supports, one at each end...)
Then print the 10mm Part 1 and Part 2 - approx. one full middle support for every 1000mm (40") of shelf - i.e. support every 500mm (20").
Printed in PLA and they snap together tightly - if using a glass shelf longer then 1000mm (40"), I suggest you glue the two pieces (Part 1 and Part 2) together.
Theoretically, you can use as many 10mm assembled middle supports as needed for your length of glass/plexi shelf.
The Sketchup files are included, if you wish to change the dimensions for your needs.