Got this sketching kit today, but I don't know what the grey cube

EGOSONG 41 Drawing Set Sketch Kit, Sketching Supplies with Sketchbook, Graphite, and Charcoal Pencils, Pro Art Drawing Kit for Adults Teens

Prina 50 Pack Drawing Set Sketch Kit, Sketching Supplies with 3-Color Sketchbook, Graphite, and Charcoal

General's Drawing & Sketching Kit #20 - FLAX

Royal & Langnickel - RSET-LT252 - Learn to Sketching 31pc Set

sketching set 26-piece kit, Five Below

Drawing Pencil Set Sketching Kit, Sketch Pencils and Sketch Pads Art Supplies With Drawing Pad Charcoal Paper in Art Carrying Case

Classic Sketching and Drawing — Nature's Workshop Plus

Drawing Pencils for Sketching Shading Blending Crafting Drawing Supplies Sketching Kit Sketch Book, Coloring Book, Metallic Pens - AliExpress

Current Sketching Kit - October 2022 - Liz Steel : Liz Steel

28/54/72/96/144 Pcs Drawing Sketching Coloring Set Drawing Pencils and Sketching Kit Art Tool Kit Professional Art Supplies Set - AliExpress