BUILT-IN HORIZONTAL SLIDING UNIT (Sill Supported) WRITANIUM® MARKERBOARDS A perfect fit. We customize our Built-in Horizontal Sliding Units without housing to use in your existing cabinetry. Choose from any of our tackable or writing surface options. Porcelain-on-steel writing surfaces with a lifetime warranty. Available in either top support (THS) or sill support (SHS) sliding panels. Heavy duty aluminum extrusions come standard in clear satin anodized. Select alternative finishes in dark bronze anodized or powder coated options. Safety first: radius blade tray ends equal no sharp edges.