These have a 1/4" mounting stud and a 1/4" to 3/8" bushing to fit both 1/4" and 3/8" spiders. The smaller diameter mounting stud reduces the weight by 50%. They utilize set screws for adjustment and the proper size hex key is supplied.
AstroSystems is the largest supplier of secondary holders and spiders to the astronomical community. There are no tools needed to adjust holders of 2.6 inches or larger in minor axis size; they come standard with thumbscrews. Holders from 2.1 inches and smaller are supplied with a hex key that gives positive seating in the hex screw even in the dark. All sizes feature our innovative four screw/two-axis adjustment that greatly simplifies collimation. With a four screw adjustment, each screw is centered between the spider vanes, making collimation adjustments a snap. Two nuts with nylon washers position the holder laterally and also allow easy adjustment of the rotation. The secondary mirror is held securely yet safely against the front lip of the aluminum bezel with polyester batting. Available in 19 sizes, ranging from 1.3 inch to 7.0 inch. Use the link below for dimensions, exact weight and sizing.