We use milk, buttermilk or yoghurt cartons from the supermarket as convenient moulds for our square designs. To help the soap batter to run down the center stainless steel rod, we use a small funnel. But without this holder, the funnel sits too deep in the mould and you can not see properly.
Add this little gadget and problem solved. We even reduced the width on one side for maximum view. The center hole is around 12mm.
If you need a different size, then let us know!
This tool is printed with PLA.
How to use, see this video.