There are two types of 6.5 aftermarket speakers available. (see 6.75 Oversize also)

The difference is within the Inner Mounting Diameter.

These have inner Mounting Diameter of 5.1 - 5.3 Inches.

These have a 16cm woofer (the other type) are known as Oversized and are 6.75.

Most Component type are 6.75 or 16.50cm woofer sized

Some Speakers are Convertible

(Meaning they have smaller Inner Diameter but also have wings to allow 6 7/8 Mounting Options
1. Look at Photo for example of a Convertible Type speaker.
2. This speaker has the conveniences of being able to fit into tight locations, and able to be flexible with mounting options.
3. Also, Mounting Depth is extremely important. Having too deep a speaker can result in some issue, speaker adapters are handy for this.

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   6.5 Car Speakers Door 2way 200w Shallow Slim Mount: Pioneer TS-F1634R FD

   (6.5" 16CM) DOOR SPEAKERS:(Mounting Depth: 1-5/8" / 41mm)

   $29.99

   

   BMW Aftermarket Radio Wire Harness Install Stereo 470-BMW

   Select: 90, 91, 92, 93, 94, 95, 96, 97, 98, 99, 2000

   $8.95

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