Unique Bargains Unique Bargains Silver Tone Concave Convex R15-25mm Radius Gauge Gage Measure ToolCategory: Tone Concave DiscRadius gauges require a bright light behind the object to be measured. The gauge is placed against the edge to be checked and any light leakage between the and edge indicates a mismatch that requires correction. It is a kind of observational measurement because of its visual test way. R15-25mm includes 16pcs at each end, radius as 15mm, 15.5mm, 16mm, 16.5mm, 17mm, 17.5mm, 18mm, 18.5mm, 19mm, 19.5mm, 20mm, 21mm, 22mm, 23mm, 24mm, 25mm. For CALIFORNIA residents only: WARNING: This product contains chemicals including DEHP, which is known to the State of California to cause cancer and birth defects or other reproductive harm.Please note that by posting this Proposition 65 warning, we are notifying you that one or more of the Proposition 65 listed chemicals may be present in a product. With Unique Bargains' products, the exposure to these chemicals may be of no significant risk to you, but out of caution, we have elected to place this warning on our site to make sure our customers are informed.You can find more infomation at http://www.oehha.ca.gov/proposition-65/about-proposition-65.