fit into a recess 68 in the bottom of the element 60 as also illustrated in fig5 the pins 62 provide the spacing between the hexagon elements the lengths of the pins 62 are dimensioned so that they go partly into the recesses 64 so that the extending ends of the pins contact flat sections of adjacent hexagon elements the loosely fitting pins 62 in the recesses of the hexagon elements maintain the spacing between the hexagon elements as the beryllium powder in the container 58 is being compressed the bottom pins 66 in recesses 68 provide space on the bottom of the structure 56 and provides means for drilling and removing the mandrels after the beryllium body is formed after the beryllium powder has been added to the container 58 a cover 70 is welded thereon this was the step 18 illustrated in fig1 fig5 illustrates the various positions of the material tooling and container during the hot isostatic pressing operation illustrated as step 26 in fig1 the spaced hexagon elements 60 are disposed within the container 58 with the cover 70 spacing between the elements 60 are provided by the spacer pins 62 to receive beryllium powder therebetween fig6 illustrates the beryllium powder 72 in the spacing between the hexagon elements 60 the positions of the pins 62 are illustrated in this figure the pins 66 disposed towards the bottom of the beryllium body to be formed are also illustrated fig7 illustrates the final form of the beryllium body or mirror after the mandrels comprising the hexagon elements have been removed as illustrated in step 42.