Another thread was started recently asking about aluminum main caps for big blocks, but I don't want to hijack that one simply cuz I want to change the direction of the topic a bit.

The first aluminum main caps of which I am aware were / are what Indy Cylinder Head came out with in the '90s, IIRC. They're fabricated from aluminum plate (not sure using what material type) and certainly appear "beefy". However, their design results in a variety of stress concentrations (a.k.a. stress raisers / risers) due to the sharp edges & corners left during machining.

The design that Best Machine and BCR / SDC use for their respective standard-replacement caps eliminates some of the stress concentrations found in the Indy design, but still leaves some primarily around the mounting surfaces for the studs' washers & nuts. BCR / SDC also has a different style cap for use with their specific girdle, but it shares the same characteristics where they're held down. I believe the Best Machine caps are (were) made from 7075 heat-treated aluminum, but don't know what the BCR / SDC caps use.

The style of caps which may be manufactured by Stanke Motorsports and also sold by 440 Source and Mancini Racing take this a step further in that the the mounting surfaces for the studs' washers & nuts is basically flat with a smooth(er) transition into the bridge area. I believe these are made from 7075 heat-treated aluminum, as well.

My backup block was machined years ago with a set of the Indy Cylinder Head main caps because that's what I could find at the time. However, my concerns increased about their durability over time in a street/strip application, so I worked with Michael Doty (Doty Manufacturing, Inc.) later to modify the caps to remove the obvious stress concentrations mentioned above.

The drawback I see is that we've reduced some of the "bulk" in the main part of the cap. However, I'll be using them with a "budget" girdle w/ hope it's a Band-Aid that adds stability in the same approach as another Moparts member has done with their build that used the standard BCR / SDC caps. Pic below is of that build, not mine (which has not been started as of this post).

I would pointedly question the need to design in a threaded blind hole in likely the highest stress area of a main cap. I suppose a lot depends on what forces and vectors are in play that a girdle as pictured is tasked with removing or reducing.
I'd lean towards no center threaded gridle bolt and leave the cap robust unthreaded and rely on the main studs to help locate the cap.

I’d like to see the Stanley caps installed in a block, to see how #5 clears the rear main seal.

I'd imagine with any of these designs, that the block would most likely fail before the caps.

I believe it's there to aid in removal using a slide hammer.

I made a bridge, that removes the cap evenly. My INDY block uses billet steel caps, and it's the only way to remove them. My bridge is setup to do aluminum caps in a iron block as well.

Good point. In my uneducated opinion, the best way to help a stock block would be a very extensive scurt extension, on the order of two to four inches. Increase the pan bolt size if possible, and now you would have a rather large, thick girdle that transfers loads to the pan rail in virtucal as well as horizontal directions. I assume the cost of this would be quite high, and only be worth it in a case where a stock block was required. Resleeving the whole block with the best sleeves available would be on the list as well. After that, head stud strength might be the next problem to look at. The cost would be crazy high except for someone with machinery to build his own out of aluminum plate. Pan would obviously have to be a custom unit as well.

I agree, and I assume then already being there the girdle just utilized them.
But being placed at the worst location strength wise is the kicker here.
So, it that is a 3/8 thread, would 2 1/4" threads spaced a apart as possible achieve the same result with the mentioned "bridge" with little downside.
However, I'm not reading many/any reports here of any Alum caps failure to begin with, of any design.
8,75" rear caps have the same design shortcoming IMO by locating the adjuster retainer bolt dead center of the arc IMO.

I did the same thing. The main caps in my KB block are a really tight fit.
I've seen people use a slide hammer, but I like the smooth even pulling of a bridge better.

I have seen caps break due to the slide hammer tapped hole. I prefer the bridged method also with caps with no threaded slide hammer hole.

I'd agree, if I wasn't aware already of some aluminum cap failures over the years

Can people who use a bridge device(?) to remove caps please show pics? Thx

My guess was it was a robust bar long enough to span the pan rails with threaded holes each end w/long enough threaded bolts and a center hole to grab the cap, and the end bolts lift off the cap as the bolts are turned down is what I imagined.
The pics others share will tell.

I kind of think that 7075 is not the best aluminum alloy for an engine part. The strength drops in less than half from 212°F to 300°F.

https://matweb.com/search/DataSheet.aspx?MatGUID=4f19a42be94546b686bbf43f79c51b7d&ckck=1

I had wondered why T&D made their rocker arms out of 2024 rather than 7075.

https://matweb.com/search/DataSheet.aspx?MatGUID=ecf8530875cb4ded9675b827f77bfac5

All alum strengths are very temp dependent. The two tables you share indicates I believe 7075 at 312F still exceeds 2024 tensile strength by more than 10%, so not sure what point you are making here.

I don't know enough to debate the better choice of alloy for two very seemingly different load/fatigue applications, rocker vs main caps.