SAFETY HOURGLASS TIMER: The large color 3/5/10/15/30 minute sand timer made by friendly high borosilicate glass and plastic material. And each sand watch 3/5/10/15/30 min has a number of time mark. easy to distinguish which timer for which usage. Size: 5.2 X 2.6 inch NON-BREAKEBLE SAND TIMER: The hourglass outer layer is made of friendly plactic and the inner one is made of glass, which is protected by double layer. And the hexagonal top caps are firm & durable, so it's more sturdy and secure avoiding moms' worry BEST TIME MANAGEMENT TOOL: The sand timers for classroom 3/5/10/15/30 minute help your kids do things more efficiently and develop a strong sense of time. The 3/5/10/15/30 minute hourglass can be used for cooking, games, classroom, study, desk office decorative WARM TIP: This 3/5/10/15/30 minute hourglass sand timer is mainly made for games, which is not a precision timing device, so there is time deviation.