Subs,overshot,

In wireline drilling, the overshot and subs are the specialized retrieval and connection components that allow for core recovery without pulling the drill string.
1. Core Barrel Overshot
The overshot is a mechanical recovery tool lowered on a wireline cable to retrieve the inner tube from the bottom of the hole.
Latching Mechanism: It features heavy-duty “lifting dogs” (jaws) that snap onto the spearhead of the inner tube’s head assembly.
Release Feature: Most modern designs, like the Boart Longyear Roller Latch Overshot, include a safety release. If the inner tube is stuck, the driller can trigger a release to avoid breaking the wireline cable.
Swivel Function: It typically includes a heavy-duty swivel to prevent the wireline cable from twisting as it is lowered or hoisted.
2. Core System Subs (Adapters)
Subs are short, threaded transition pieces used to connect different components of the core barrel or drill string.
Adapter Subs: These connect the drill rods to the outer tube of the core barrel. They ensure the high-torque rotation of the rods is transmitted smoothly to the barrel.
Saver Subs: Placed between the drill rig’s top drive and the first drill rod, these take the wear of constant threading and unthreading, protecting the more expensive rig components.
Inner Tube Subs: Sometimes used to adjust the length or “space out” the inner tube assembly to ensure the core lifter is positioned perfectly relative to the diamond bit.