penetration interlock
Penetration where the thing that is penetrating (usually a penis) is in turn being penetrated (through the urethra if it's a penis) while inside. To avoid confusion, these will be referred to as the socket, being penetrated by the barrel, which is in turn being penetrated by the pin, using barrel connectors as a metaphor.
Usual scenarios
This can happen in a number of ways, so here's a list of common cases and how they look in practice.
Case #1: "Coaxial mating"
post #6251587 post #4638943 post #3747412 post #3153618 post #3260081 post #5857594
The most common case, this is where the pin and socket are actually "together" (usually meaning they belong to the same person and/or two parts of the same organ). This can range from things like fellatio with urethral tonguing, slit sex, performing a face-in-sheath fellatio, or a penis milking machine with a "straw" on the inside. While almost all these examples involve urethral penetration, that's only because penises are by far the most commonly used type of barrel, and urethral is not a requirement.
Case #1b: "Concentric mutual penetration"
post #1155768 post #4376248 post #5609477
A rarer situation where penetratration interlock is more or less exploited to allow both partner to fully penetrate one another to the hilt (which usually restricts this to slit sex or intravaginal penis) in a symmetrical manner. Not to be confused with the likes of slit sounding/sheath sounding, which are closer to recursive penetration (even though they are specifically excluded from the definition).
Case #2: "Floating pin"
post #3975401 post #2437647 post #2514605 post #3790587
This is when the pin is not actually "attached" to either side, which usually translates to it being some kind of dildo, a parasite, or a character small enough to fit inside the socket.
Case #2b: "Insertion loss"
Similar to the above, but where the pin is actually removed from the socket in the process. This most frequent with infestation, but can also occur with vore as part of prey transfer, and possibly with some form of "reverse oviposition" style egg theft.
Note the second example above, post #2512088, which uses partial vore to make the barrel the vagina of a second pred. While almost always the case, the barrel doesn't need to be a penis (or penis-like organ like an ovipositor or pseudo-penis).
Case #3: "Secure cum channel"
post #2038080 post #5665995 post #4605817
Some form of meeting in the middle, which ends up with both penetration interlock (from the barrel's perspective) and recursive penetration (from the pin's perspective). Can border on thread transfer if the pin is doing most of the distance, like in post #5665995, although both probably shouldn't be tagged together.
Case #3b: "Full-duplex penetration"
Similar to the above, but one side is doing a full all the way through penetration, and being penetrated the other way as it emerges. This counts as penetration tunneling, but even though it's technically interlock from the barrel's perspective, is less commonly tagged as such.
Visual Guide
| Name | Diagram |
|---|---|
| Penetration Tunneling | ════╗ ────┐ ▌ ▌ █████▌ ▌ ────┘ ▌ ════╝ |
| Recursive Penetration | ════╗ ───┐ ║ ▌ ▌ ███████▌ ▌ ───┘ ║ ▌ ════╝ |
| Penetration Interlock | ╔══════ ───┐ ▌ ▌ ██████▌ ▌ ───┘ ▌ ╚══════ |
| Penetration Interlock + Recursive Penetration | ╔══════╗ ───┐ ║ ▌ ║ ▌ ██████████▌ ║ ▌ ───┘ ║ ▌ ╚══════╝ |
