Standard Block Dimensions   1.5"W x 1.5"H x 1.75"L.   These blocks are optimal for bullets in the 180 - 300 grain range, depending on alloy.   300 to 425 grain bullets are sometimes made in these blocks but heat-related fill problems may occur, depending on alloy, mold material, and casting technique.   As a single cavity, the standard block cast well with 400 - 700 grain bullets.
XL Block Dimensions  1.5"W x 1.5"H x 2.25"L.   The XL blocks are mandatory for 2-cavity 50 caliber molds.   In addition, the XL blocks may be a prudent option for any bullet over 325 grains.
Handles  are not included. RCBS handles will fit, Lee 6-cavity handles will fit, and current production Saeco/Lyman handles can be modified to fit.
Aluminum  aircraft alloy is light weight, corrosion resistant, and easy to machine.   Aluminum seems to be better than other materials at avoiding overheating problems when casting very large bullets.   On the down side, all aluminum alloys loose much of their strength at bullet-casting temperatures.
Brass   Brass resists corrosion and machines beautifully.   Brass has the highest thermal conductivity of any of the mold materials, which sounds good in theory but doesn't seem to make a darned bit of difference in practice.   On the downside, brass is heavy.   Being cold rolled, it does have residual stresses and it can warp a tiny bit after machining, though very rarely does it warp enough to create a noticeable problem with standard size blocks.   However, because of the warping and the weight, I do not use brass for XL blocks.   Also, I do not recommend brass for black powder applications, since the high casting temperatures make it more prone to warp.
Sprue Plates  are made from 1/4" heat treated 4140 steel.
Alignment   Stainless steel male/female bushings.
Ventilation   Vent lines are cut on both halves of the block.   I have made several unvented molds for my own use that cast as well as any other, but some alloys show a distinct preference for aggressive venting, especially at higher mold temperatures.