Mark WP #41-A is a rare mark.

The mark is comprise of an encircled Itarii 伊 symbol with the symbols Sa サ and Do ド above of the circle.

This mark has only been found on Sado Island.

All of the floats with mark WP #41-A are heavily worn; this float is not an exception.  It's has many scratches in the glass and lots of remnants of sea life.  

The ID seal has some major chipping on the bottom of it but just the bottom of the circle is missing.  All points of the Itarii 伊 symbol are showing. Fortunately, the Sa サ and Do ド symbols are also clearly visible.  These symbols are often mis-stamped, partial, or even missing on some of the other examples of WP #41-A I've seen.

This float is 44 3/4 in circumference or about 14 1/4 inches in diameter.  It's larger than the 13 inch size described in Walt Pich's 'Glass Ball Marks' book.  I'm not sure how or if that effects it's rarity.

It also has excellent provenance having been found by Kala & Aragon Ellwanger on Sado Island, Japan in 2019.