What is this called?

[Rusty Nail]

Was missing the bolts that are found on the front of the spring.. was shaking and loose, making a rattle.

2.5" springs.
I bought 2 x 4 inch, 3/8 ×16 bolts and nuts.

How tight should it be? I assume tight enough to not work loose but not tight enough to cause a bind, but WTF is it? WTF does it do?
I only ASSUME the bolts were missing because jumping? Whatever.

When I tightened them to the above spec, the whole dealy got very stern and refused to budge. That's good , right? It's what I want fer sure, are there any adverse effects? What else just changed, if anything?

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Driver side

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Passenger side

 

[Snoots]

Honestly don't know what they are called but mine has them too. The bolts are tight but not so tight that they bend the 'ears'.

 

[Honky Kong jr]

I’m thinking they are there to keep the spring pack aligned.

 

[74 Shortbed]

I’m thinking they are there to keep the spring pack aligned.

Yup...

 

[smoothandlow84]

X3 yup...they just keep the packs together so the individual springs don't spread apart.

 

[chengny]

Those are called rebound clips. They are designed to make all the leafs share the load - but only on those rare occasions when there is a downward load created by the weight of an unsupported axle - and not overload the main spring:

The leaf springs are normally installed with the band forward of the axle, but it is not something that has to be done that way. The steel band is called the rebound clip. Their main purpose is to help keep the main leaf from breaking on a rebound.

When the weight of a vehicle or trailer is on the spring, all of the leaves work together to support the spring above them. If the wheel drops for any reason the total weight of the axle falls on the main leaf if there are no rebound clips. The clip also keeps the leaves neatly stacked.

 

[Rusty Nail]

Thank you @chengny .

 

[Honky Kong jr]

Those are called rebound clips. They are designed to make all the leafs share the load - but only on those rare occasions when there is a downward load created by the weight of an unsupported axle - and not overload the main spring:

The leaf springs are normally installed with the band forward of the axle, but it is not something that has to be done that way. The steel band is called the rebound clip. Their main purpose is to help keep the main leaf from breaking on a rebound.

When the weight of a vehicle or trailer is on the spring, all of the leaves work together to support the spring above them. If the wheel drops for any reason the total weight of the axle falls on the main leaf if there are no rebound clips. The clip also keeps the leaves neatly stacked.

Top notch as usual

 

[Frankenchevy]

but only on those rare occasions when there is a downward load created by the weight of an unsupported axle - and not overload the main spring

see. gm intended for you to get air in these trucks