In my professional opinion, the following item is:

#299 Ten Cent Pan-American. Bottom Plate Block of 6.   

I grade this item: Medium Fine 3, which means:

Well-Centered. Hinged Original Gum. Top stamps with heavy hinge remnants, bottom stamps are Never Hinged.  Also hinged in the selvedge at bottom.  Very Scarce.

Scott Catalog Value for OG: $6000

Thank you,

Karl Anderson

Anderson Stamp & Coin

POB 51258, Provo, Utah 84605

APS #130744.  I am a full-time stamp and coin dealer; and a regular advertiser in Linn's Stamp News and Coin World Publications (since 1975).