Kickback may also occur as a result of a failed or improperly executed boring cut. Bore cutting is a specialised technique requiring proper training, and should not be attempted without such training. By far the most effective tool in preventing kickback is operator training. By preventing contact between the bar tip and solid objects, kickback may be avoided. By keeping their head and body out of the cutting plane of the bar, injury may be prevented if kickback occurs. A useful tip is that if the operator can't read the logo on the side of the bar, they are too close to the cutting plane and should lean left to ensure safety. Correct chain sharpening is paramount to safety in this context. Blunt chain cuts poorly and leads to increased operator fatigue and increased bar loading. Depth gauges filed too low make the chain grab at the wood and may negate the benefits offered by safety chain. Chain design plays a major part in kickback reduction. Older, non-safety designs carried only teeth and depth gauges. Since these present a solid leading edge at the depth gauge should an object be suddenly forced into the chain, they can easily be made to engage fully with the foreign body and launch into a full kickback. Careful filing of the depth gauges, making a radius down to the leading edge, reduces the risk somewhat. Newer chains with ramped drive links fill in the gap ahead of the depth gauge, reducing the tendency to grab still further. Full safety chains have extra bumper links between the cutting links, maintaining nearly full depth gauge height along the full extent of the chain and reducing the risk of kickback to very low levels. Full safety (bumpered) chains are often fitted as original equipment to domestic and entry level saws. Modern "professional" chains offer far higher cutting performance than full safety chain, and offset their increased risk with an assumption of a much higher degree of operator competence. In reality they are still safer than traditional chains due to the vastly improved depth gauge design, with a deep ramp ahead of the gauge point. Bar design is another factor in reducing kickback risk. The larger the radius of the bar tip, the greater the risk of kickback as the degree of engagement with the log (or other body) will be greater for a larger tip. Domestic class bars, climbing saw bars and entry-level professional bars usually have very small tips. Professional bars designed for logging and felling may have much larger tips as they are often used for boring cuts to free trapped timber or fell difficult trees, and a tapered, small-tipped bar will wedge easily when boring, stalling the chain.