ROUND LEVEL 1 CLEAR-VISION BULLET RESISTANT ACRYLIC SPEAK-THRUVirtually Unobstructed Vision, Disc Overlap Prevents Direct Entry of Projectiles While Allowing Natural Voice Transmission.Clear Vision Bullet Resistant Speak-Thrus not only offer two levels of protection but provide a clear field of vision. The unit is easy to install. Just drill a six inch (152 millimeter) diameter hole in the bullet resistant window, surrounded by three 5/16 inch (8 millimeter) holes spaced at 120º on a 7-1/2 inch (190 millimeter) diameter (template included). Then secure the 10 inch (254 millimeters) Acrylic or Laminated Polycarbonate Disc using the Brushed Stainless Steel Studs provided with the unit. The space between the window and disc allow for clear voice transmission. The 10 inch (254 millimeter) disc provides enough overlap to prevent direct entry of projectiles.