Specially hand-ground for maximum precision. The flat spots allow the setscrew to better settle into the coupling. XRAY T2'06 XRAY T2'06 XRAY T2'07 EU XRAY T2'07 US XRAY T2'08 XRAY T2'08 EU XRAY T2'08 US XRAY T2'09 EU XRAY T2'09 US XRAY T3'10 XRAY T3'10 EU XRAY T3'10 US XRAY T3'11 XRAY T3'12 XRAY T4'13 XRAY T4'14 XRAY T4'15 XRAY T4'16 XRAY T4'17 XRAY T4'18 XRAY T4'19 XRAY T4F'20.