Most Stratocaster® bridges fall into 3 categories: American Standard (2 pin tremolo), Synchronized (6 screw tremolo), and Fixed (hardtail bridge, no tremolo). Hipshot makes replacement bridges for each of these.
American Standard (2 Pivot) Tremolos:
The american standard tremolo system uses two pivot posts and a spring cavity on the back of the body to keep the bridge in place and allow for full floating action. Full floating means the strings can be raised in pitch and lowered in pitch by pulling the tremolo arm up or down. Depending on how the bridge is setup, it can also be "dive only" - meaning it can't raise in pitch when pulled back.
Hipshot makes two bridges that fit this type of guitar, the US Contour and the US Flat Plate. The main difference between these bridges is aesthetics.
Many brands including Fender® Gotoh®, Wilkinson® and Schaller® use the same mounting pattern. Floyd Rose® does not use this pattern. The Hipshot US Contour and Flat Plate are not compatible with Floyd Rose®.
Synchronized (6 Screw) Tremolos:
The Synchronized tremolo, Named by Leo Fender in his original patent design, uses 6 screws to affix the bridge to the guitar along with a spring cavity on the back to counteract the tension of the strings. The 6 screws also act as pivot points.
The Hipshot Synchronized tremolo is designed to fit Fender guitars, of which there are two varieties: .416 (Narrow, Modern, 2 1/16 in) and .430 (Wide, Vintage, 2 1/8 in)
To find out which fits your guitar, you should consult the dimensions.
Hard Tail (Fixed Bridge)
The Fixed Bridge or Hard Tail Stratocaster does away with the spring cavity and pivot mechanism. Instead the bridge is affixed directly to the body with 3 screws. The strings are guided through the body from the back and up over the saddles.
There are two different string spacings of this bridge typically made by Fender: Wide and Narrow.
The Hipshot Hardtail bridge comes in wide and narrow to suit the two options. To determine which one is the correct size, it is recommended to consult the dimensions.