Mine is a pressing clapper. Years ago I overheard a conversation at a quilt show about the winning quilter never presses her seams without using one. I had no idea what it was so I butted in and asked. At that time June Tailor was making them. It makes a big difference in my blocks, all the seams are flat and smooth. I use it on every seam I press. Before I found the wooden one to buy, I used my smooth bottom bacon press, (I never used anyway) :D One of the old flat irons would work for quilt seams too. It really makes a difference to use one.
Here is link to a picture and how to use it:
http://www.judisstudio.com.au/index....d=22&Itemid=34
I haven't found any June Tailor Clappers in a long time. Ebay may have them.