core bit for NQ HQ PQ wireline systems

Wireline core drilling is the standard method used across mineral exploration, geotechnical investigation and environmental sampling. At the heart of every wireline run is the core bit — the cutting element that grinds through rock and shapes the core sample that reaches the surface. For crews working with NQ, HQ and PQ wireline systems, the choice of core bit has a direct effect on core recovery, penetration rate and the cost of every meter drilled.

This guide explains how NQ, HQ and PQ wireline systems work, what each size is best suited for, and how to pick the right core bit for your formation and drilling program.

What is a wireline core drilling system?

In conventional core drilling, the whole drill string has to be pulled from the hole every time a core sample is taken. A wireline system changes this. The core barrel is carried inside an inner tube that is lowered and retrieved on a wireline cable, so the drill rods stay in the hole. This saves a large amount of trip time, which is why wireline coring is the preferred method for deep holes and high-production exploration programs.

The wireline system is built around a set of standard sizes, and each size is defined by the diameter of the core it recovers. NQ, HQ and PQ are the three most widely used sizes in exploration and geotechnical drilling. The core bit you fit to the bottom of the string must match the system size exactly, because the bit controls both the hole diameter and the diameter of the core that enters the barrel.

NQ, HQ and PQ core bit sizes at a glance

Each wireline size has a fixed bit outer diameter and a fixed core diameter. Matching these dimensions keeps the core barrel, reaming shell and casing working together as one string.

NQ is the workhorse of deep exploration because a smaller bit means less torque and faster penetration in hard rock. HQ offers a larger, more stable sample and is common in civil engineering and dam projects. PQ produces the largest core and is chosen when the formation is broken or when a bigger sample volume is needed for testing.

Core bit types used on wireline systems

The right bit type depends mainly on the hardness and abrasiveness of the rock you are drilling. The most common options for NQ, HQ and PQ wireline systems are:

Impregnated diamond core bit. Diamond is mixed throughout the matrix rather than sitting only on the surface. As the matrix wears, fresh diamond is exposed, which keeps the bit cutting in hard, abrasive rock. This is the most widely used type for deep exploration in quartzite, granite and other hard formations. A well-matched impregnated core bit gives steady penetration and long life in these conditions.

Surface set core bit. Larger diamonds are set on the face of the bit. It cuts quickly in soft to medium formations but has a shorter life in abrasive rock, because the surface diamonds wear down and are not replaced.

PDC core bit. Polycrystalline diamond compact cutters are brazed onto the bit face. PDC bits are a good fit for soft, clay-rich and medium formations where they deliver high penetration rates and long service life.

TSP and electroplated core bits. Thermally stable polycrystalline (TSP) bits suit medium-hard rock, while electroplated bits are an economical option for soft formations and shallow drilling programs.

How to choose the right core bit for your program

Start with the formation. If the rock is hard and abrasive, an impregnated design with the correct matrix hardness is usually the best choice. For soft ground, a surface set or PDC bit will cut faster and keep costs down. If the formation varies, a bit that handles mixed conditions — or a quick change of matrix grade between runs — will protect both penetration rate and core recovery.

Next, confirm the system size. The bit must match the NQ, HQ or PQ wireline barrel you are running, including the thread connection and the reaming shell that sits behind the bit. A mismatched bit damages the barrel and wastes drilling time.

Finally, balance penetration rate against bit life. A softer matrix wears faster but cuts quicker; a harder matrix lasts longer but may polish in soft rock. Experienced suppliers can recommend a matrix grade for your specific rock type, and many offer custom designs for unusual conditions.

Matching accessories complete the string

A core bit never works alone. Reaming shells keep the hole gauge open behind the bit, casing shoes and casing bits seat the casing in overburden, and core barrels, core lifters and core trays protect the sample on its way to the surface. Ordering the bit together with its matching accessories avoids compatibility problems in the field and keeps the whole string running smoothly.

Why choose TY Drill Bits for NQ, HQ and PQ coring

Xi'an Heaven Abundant Mining Equipment Co., Ltd. (TY Drill Bits) has manufactured and supplied drilling tools from Xi'an, China since 2010. The company covers PDC bits, tricone bits, core bits, rock drilling tools and related accessories, and holds ISO9001 certification. Core bits are available in NQ, HQ, PQ and other standard sizes, including the popular NQ impregnated diamond core bit, HQ and PQ impregnated designs, surface set, TSP, PDC and electroplated types.

Because the company is a manufacturer rather than a trading house, buyers can request custom matrix grades, crown profiles and dimensions to match their drilling conditions. OEM service is available, and standard orders ship within 15 working days. The sales team works with buyers on FOB, CFR, CIF and other incoterms, with payment by T/T, L/C or other agreed methods.

Final thoughts

The core bit is a small part of the drill string, but it decides how fast you advance, how clean your samples are and how much every meter costs. Understanding the NQ, HQ and PQ wireline sizes, choosing the right bit type for the formation, and matching the bit with the correct accessories will keep your exploration program on schedule and on budget.

If you are planning a coring program and need help selecting the right core bit for NQ, HQ or PQ wireline systems, contact the TY Drill Bits team with your hole size and rock type — they can recommend a bit and matrix grade that fits your conditions.