Tailor's clapper is a pretty great tool to have by hand if you want sharp and neat results when you press your seams.
It is made of oak which makes it rather weighty.
Start by steaming your seam. Place your clapper on the seam for 5-10 seconds to allow it to slowly absorb the steam while allowing it to do the work in the fabric.
It's excellent to use for wool, silke, viscose etc. to avoid shiny seams after pressing with your iron.
It measures 21x9 cm and is 5 cm withouth the handle.