Legamaster Separation Tape Black - Width 3mm, 16 m for clear and easy lines on whiteboards or glassboards - easy removeable whiteboard tape : Amazon.co.uk: Stationery & Office Supplies
Whiteboards + Podiums - Storr Office Environments
How to create lines on a whiteboard
Amazon.com: StoreSMART® - Magnetic Lines and Board Dividers - Half-inch x 25-feet - for Whiteboard Grids - ML1/2-25 : Everything Else