Undersized flash hole decapping die

Hi, saw this and was wondering in what scenario would I need something like this? I’m guessing it has a smaller decap pin diameter.

Hm. Not just a small primer? Don’t know what this is.

Lee Precision, Inc. - Undersize Flash Hole Universal Decapping Die

I use Lapua brass for 6.5 Creedmoor, small rifle primer pockets. My RCBS decapping die was too thick for the small flash hole in the Lapua brass. Someone told me to get the Sinclair decapping die with the smaller decapping pin size, part #749-008-885. They claim it is for 0.060 inch flash holes. It works. I measured the RCBS decapping pin at 0.0695 inches. The Sinclair decapping pin measures 0.0560 inches.

Hope this helps.