July 11, 2026 · Drillstrings Team
Downhole tools are the specialty components that go into the BHA to control trajectory, protect the string, and free stuck pipe — jars, stabilizers, crossover subs, and shock (or shock-absorbing) tools. Because they run in a high-stress, hard-to-reach part of the well, a bad rental tool is expensive: a failed jar during a stuck-pipe event or a washed-out sub can cost days. This checklist covers what to confirm before any rented downhole tool leaves the yard.
Before anything: match the tool to the well
For every item, confirm four basics against your BHA design and well plan:
- OD and length fit the hole size and the position in the string.
- Connection type (NC38, NC46, NC50, etc.) matches the mating components — box and pin.
- Pressure and temperature ratings exceed the well’s expected maxima.
- Service — if the well is sour, tools contacting the wellbore must meet NACE MR0175 / ISO 15156 for H2S service.
Drilling jars
A drilling jar delivers an impact load up or down to free stuck pipe. It is the tool you hope never to need and cannot afford to have fail.
- Confirm jar type (hydraulic, mechanical, or hydraulic-mechanical) suits the application.
- Verify trip load and impact rating against your torque-and-drag model — the jar must fire within the string’s available overpull.
- Check the service and pressure rating and the last function-test / recertification date.
- Confirm intended placement keeps the jar in tension during normal drilling (typically in or just above the HWDP).
- Ask for the pump-open force so you can account for it in weight-on-bit calculations.
Stabilizers
Stabilizers centralize the BHA and set directional tendency through their gauge and spacing.
- Verify blade OD (gauge) — an undergauge stabilizer will not control trajectory. Ask for the measured, not nominal, gauge.
- Confirm type (integral-blade, sleeve, or replaceable-sleeve) and blade design (straight or spiral).
- Check hardfacing condition on the blades — worn or missing dressing means it will wear out of gauge quickly.
- Confirm connection and OD match the collars above and below.
Crossover subs and other subs
Subs adapt connections and add function. They are small, cheap to overlook, and a frequent failure point.
- Confirm the box × pin combination exactly (e.g., NC50 box × NC46 pin).
- Check bore size for flow area and to pass any tools that must go through.
- Inspect shoulder and thread condition — subs concentrate stress and often see the most make/break cycles.
- For float subs / bit subs, confirm the float valve type and condition.
Shock (shock-absorbing) tools
A shock tool dampens axial vibration from the bit, protecting the BHA and improving bit life in hard or interbedded formations.
- Confirm the spring/damper rating matches expected weight on bit and formation hardness.
- Verify stroke length and that it suits the vibration profile.
- Check the service rating and recertification date.
- Confirm placement — usually directly above the bit or motor.
Paperwork you should always get
Regardless of the tool, insist on:
- Current inspection certificate to DS-1 (or equivalent), with the inspection level and date.
- Material/service certification — NACE MR0175 where sour service applies.
- Dimensional and connection data sheet.
- Function-test / recertification records for jars and shock tools.
- Maximum load and pressure ratings in writing.
Our quality program documents inspection standards on every rental item, and our fishing tools and handling tools carry the same paperwork discipline.
A quick pre-run checklist
- OD, length, and connection verified against the BHA.
- Pressure, temperature, and (if sour) NACE service confirmed.
- Current DS-1 inspection cert in hand.
- Jars function-tested; trip loads modeled.
- Stabilizer gauge measured and confirmed.
- Crossover shoulders and bores checked.
- Placement in the string modeled for tension/compression.
Rent or buy
Most downhole tools are natural rental items — you need a specific jar rating or stabilizer gauge for one well, then a different set for the next. Renting keeps your yard lean and puts the exact tool on the rig. For tools you run on every well, buying inspected units can lower long-run cost. We supply both across our locations and partner network.
Send us your BHA and well parameters and we will build a compliant tool list. Contact us to rent or buy the downhole tools your string needs.