When taking a shower, it is nice to set the temperature once. These tap/valve caps can be pulled out and rotated to the correct position so that the pointer faces up to indicate the right shower temperature setting.

This fits into my 30 year old taps.

Remove the caps from your taps.

Measure with calipers and adjust the scad file.

Print two white ABS bases (which include the dot pointer).

Print one red and one blue ABS cap.

File out the holes as required so the pointer fits snugly in the cap.

Put some acetone in the seams for a great seal.

Climb into the shower and adjust the shower taps so that the temperature is just right.

Snap in the caps with the pointers facing up.

Enjoy.