You are buying

a pack of 10 4mm threaded connecting screws / interscrews

male / female screws

male screw - zinc plated pan head , 4mm x 25mm , zinc plated 

female screw - nickel plated , 4mm thread

maximum connecting thickness - 45mm 

this can be made as short as 27mm by cutting the screw down

5mm hole to be drilled to accommodate the female screw