Spinners are used when trimming your pots, instead of pressing your finger down to stabilise the pot, you use this which distributes the weight evenly preventing any indentations. It is made up of two parts that spin independently, so the bottom will spin with the pot and the top where your finger presses stays still.
Spinner is 4cm
Also available are three sizes of extenders (6cm, 7.5cm, and 9cm) which can help further distribute weight, but also are great as guides for how wide to make your foot ring and ensure consistency. The three sizes will mean anything from a small trinket dish, smaller mugs, standard mugs, travel cups and up to breakfast bowls and vases will have consistently sizes foot rings.
I've found trimming up against the extender allows me to undercut the foot profile as well.
