How to Select the Right Grizzly Bar Spacing for Your Material

The Rule of Thumb

Set grizzly bar spacing equal to or slightly smaller than your downstream jaw crusher's closed-side setting (CSS).

That's the headline rule and it covers about 80% of all installations. The reasoning is simple: any material small enough to pass through the jaw at its CSS will also pass through the crusher chamber without being broken further. Sending that material through the crusher just wastes crusher capacity, energy, and wear part life. Better to drop it through the grizzly first and route it directly to the next stage.

Why CSS Is the Right Reference

CSS — the closed-side setting on a jaw crusher — is the gap between the jaws at the closest point of their stroke. It defines the maximum particle size that can pass through the jaw chamber unchanged. Any particle smaller than CSS will fall through; any particle larger than CSS will be crushed at least once.

When you set the grizzly bar spacing equal to CSS, you're saying: "Anything that doesn't need crushing should bypass the crusher entirely." The grizzly catches those particles before they enter the chamber and routes them around it. The crusher only sees material it actually has to break, which is exactly what you want.

Set the bar spacing larger than CSS and you'll send some "ready-to-pass" material through the crusher anyway — wasting capacity. Set it much smaller than CSS and you'll unnecessarily route some material that could have been crushed around the crusher — slightly reducing your saleable product fraction. Setting it equal to CSS (or just below) is the optimum.

Adjusting for Feed Conditions

The CSS rule is the starting point. Real feed conditions push you to adjust the spacing up or down from that baseline.

Adjustment 1 — Fines content

The percentage of feed material below the cut size determines how much benefit the grizzly delivers and how much spacing matters.

• Low fines (under 10%): Use spacing equal to CSS or slightly larger (CSS + 10–20 mm). The grizzly is mostly there to catch occasional oversized boulders; fines bypass is a marginal benefit.
• Medium fines (10–25%): Use spacing equal to CSS. This is the standard case and the bar spacing rule of thumb applies directly.
• High fines (25–40%): Drop spacing to CSS minus 10–20 mm. The high fines fraction means there's a lot to gain by tightening the spacing — the additional bypass material is worth the slight loss in screening efficiency.
• Very high fines (40%+): Drop further to CSS minus 20–40 mm, or consider perforated wear plates instead of bars. At this fines fraction, you're primarily using the grizzly as a fines bypass, not just an oversize protector.

Adjustment 2 — Feed material hardness

Hardness affects how much value you get from each ton of bypassed material:

• Hard rock (granite, basalt, quartzite): Wear part savings are very significant. Use CSS spacing or tighter to maximize bypass.
• Medium-hard rock (limestone, dolomite): Standard CSS spacing. Wear savings are still real but less dramatic.
• Soft rock (sandstone, gypsum): Wear savings are smaller per ton, so going much tighter than CSS doesn't pay back. Stick to CSS or slightly looser.

Adjustment 3 — Moisture and stickiness

Wet or sticky feeds change the math entirely:

• Dry feed (under 4% moisture): No adjustment. Use the CSS rule directly.
• Moderately wet (4–8% moisture): Open the spacing slightly (CSS + 10 mm) to reduce bridging risk. Stepped grizzly bars handle this case well.
• Wet, sticky, or clay-bound (8%+ moisture or any clay content): Open the spacing further (CSS + 20–30 mm) and consider switching to perforated wear plates or a finger-screen design. Tight bars on sticky feed will plug almost immediately.

Adjustment 4 — Plant downstream layout

Where the bypass goes also matters:

• Bypass joins the product belt directly: The bypassed fines must already be at saleable specification. Use tighter spacing only if the bypass fraction meets your finished product spec.
• Bypass routes to the secondary stage: No size constraint — the secondary crusher will resize the bypass material. Use the CSS rule freely.
• Bypass goes to a separate stockpile: Standard CSS rule applies.

Worked Example 1 — Limestone Quarry, Standard Conditions

Given: 400 t/h limestone aggregate plant. ROM is 0–600 mm with approximately 18% fines below 80 mm. Downstream: jaw crusher with 100 mm CSS. Feed is dry (3% moisture). Bypass joins the secondary stage.

Application of the rules:

• Baseline: CSS = 100 mm → bar spacing baseline = 100 mm.
• Fines adjustment: 18% fines is in the medium range → no adjustment.
• Hardness: Limestone is medium-hard → no adjustment.
• Moisture: 3% is dry → no adjustment.
• Downstream: Bypass goes to secondary → no constraint.

Selected spacing: 100 mm. Expected bypass fraction: ~18% (matches the fines content). Crusher load reduction: ~18%.

Result

An ITE1850 grizzly with 100 mm stepped manganese bars handles the 400 t/h ROM comfortably. Approximately 72 t/h of fines bypass the jaw, dropping crusher load from 400 t/h to 328 t/h. Wear part savings on the jaw plates: roughly 18%. Estimated payback on the grizzly investment: 4–6 months at typical wear part costs.

Worked Example 2 — Dirty Granite Quarry

Given: 250 t/h granite quarry. ROM is 0–500 mm with approximately 32% fines below 80 mm (the quarry has a deep weathered overburden that contributes a lot of soil and dirt). Downstream: jaw crusher with 80 mm CSS. Feed is moderately dry (5% moisture). Bypass goes to the product belt (the fines are saleable as 0–80 mm sub-base material).

Application of the rules:

• Baseline: CSS = 80 mm → bar spacing baseline = 80 mm.
• Fines adjustment: 32% fines is in the high range → drop spacing 10–20 mm → 60–70 mm.
• Hardness: Granite is hard → wear savings are valuable, push toward tighter spacing → 60 mm.
• Moisture: 5% is moderate → no adjustment, but use stepped bars rather than straight.
• Downstream: Bypass joins product belt → check that 0–60 mm meets the sub-base spec. It does (specification is 0–80 mm).

Selected spacing: 60 mm stepped manganese bars. Expected bypass fraction: ~30% (slightly higher than the 32% fines because some 60–80 mm material stays on the deck). Crusher load reduction: ~30%.

Result

A 60 mm bar spacing on this dirty granite quarry bypasses approximately 75 t/h of dirt and fines around the jaw, dropping crusher load from 250 t/h to 175 t/h. The hard granite means jaw plate wear is the dominant cost, so a 30% reduction in crusher tonnage translates to a 30% reduction in jaw plate spend — substantial savings on this material.

Worked Example 3 — Clay-Bound C&D Recycling

Given: 180 t/h C&D recycling plant. Feed is mixed concrete and asphalt rubble with significant soil and clay contamination, 8% moisture. Downstream: HSI impact crusher with 80 mm setting. Bypass goes to a separate dirt stockpile (sold as fill material).

Application of the rules:

• Baseline: Equivalent CSS ≈ 80 mm → bar spacing baseline = 80 mm.
• Fines adjustment: Mixed C&D with high contamination, but bar spacing isn't the main lever here — the issue is sticky clay. Stay near baseline.
• Hardness: C&D rubble is variable but generally moderate → no adjustment.
• Moisture: 8% with clay content → open spacing 20–30 mm above baseline → 100–110 mm. Switch from bars to perforated wear plates for blinding resistance.
• Downstream: Bypass goes to dirt stockpile, no spec constraint.

Selected spacing: Perforated AR steel plates with 100 mm openings (not bars). The plate geometry handles the sticky feed better than bars and won't blind with clay.

Result

Approximately 35–40% of the feed bypasses the impact crusher — most of it dirt and clay that the impact crusher couldn't process anyway. The HSI sees only the clean concrete and asphalt rubble that actually needs breaking. Result: dramatically fewer plugged chamber incidents and significantly extended blow bar life.

Common Bar Spacing Mistakes

Five mistakes account for almost every "the grizzly isn't working" complaint we hear.

Mistake 1 — Spacing too wide

Symptom: Crusher load is barely reduced, payback never materializes. Cause: The bar spacing is wider than the crusher CSS, so material that could have been bypassed is still going through the crusher. Fix: Drop spacing to match CSS or slightly tighter.

Mistake 2 — Spacing too tight

Symptom: Bypass fraction is too high (above the actual fines content), saleable product yield is low, the secondary stage is overloaded with material that should have gone through the primary. Cause: Bar spacing is much smaller than crusher CSS, routing crushable material around the crusher and into the bypass stream. Fix: Open spacing back up to CSS.

Mistake 3 — Ignoring fines content

Symptom: The grizzly is correctly sized to CSS but the operational benefit is minimal. Cause: Feed has very low fines content (under 5%) — the grizzly is doing its job correctly but there's just not much value in scalping such a clean feed. Fix: Honestly evaluate whether you needed the grizzly in the first place. If the feed is truly clean primary rock, a grizzly may be unnecessary and a simple grizzly feeder section would have sufficed.

Mistake 4 — Not adjusting for moisture and clay

Symptom: Grizzly blinds within hours of starting on wet feed; bars wedge full of clay; deck bridges and overflows. Cause: Spacing is correct for dry feed but the wet feed needs wider spacing or perforated plates. Fix: Open the bar spacing 20–30 mm wider, switch to perforated AR plates, or add a spray bar set at the feed end.

Mistake 5 — Locking in spacing at order

Symptom: Plant operator wants to adjust spacing as feed conditions change but can't. Cause: Original purchase specified a fixed bar set without considering future flexibility. Fix: Order a second bar set at a different spacing during the original purchase. The bars are bolted on the GELEN ITE Series so changing them takes about an hour per deck.

Bar Spacing Reference Table

Quick lookup based on jaw crusher CSS and feed type. Use this as a starting point and adjust per the rules above.

For wet/sticky feed, add 20–30 mm to the values above and consider switching from bars to perforated wear plates.

FAQ

• Can I use grizzly bar spacing larger than my jaw CSS? Yes, but you'll lose some of the wear-saving benefit. Larger spacing only makes sense if you want the grizzly purely as oversize boulder protection rather than fines bypass.
• What if my plant has multiple crusher CSS settings depending on product? Choose the smallest CSS the plant runs (the production setting that matters most). A grizzly sized for the smallest CSS still works — perhaps slightly sub-optimally — when the crusher is running larger CSS.
• How is grizzly bar spacing measured? Bar spacing is the clear gap between adjacent bars at the bar surface (not the center-to-center distance). On stepped bars, the spacing is measured at the narrowest point, which is usually the feed end of the deck.
• Does bar shape matter? Yes. Trapezoidal cross-section bars (wider at the top, narrower at the bottom) are self-clearing — stuck stones work loose downward. Rectangular bars don't have this advantage. Stepped grizzly bars combine trapezoidal cross-section with stepped longitudinal spacing for maximum self-clearing.
• How much can I change spacing in the field? Spacing changes are done by replacing the entire bar set, not by adjusting individual bars. On the ITE Series, a complete bar swap takes about an hour per deck with two operators and standard impact wrenches.

Get a Bar Spacing Recommendation

Send us your feed analysis (PSD, fines fraction, moisture), your jaw crusher CSS, and your downstream layout — we'll recommend the right bar spacing, bar material, and ITE Series model for your application.

Related guides:

• Grizzly Screen: The Complete Guide — pillar guide
• Grizzly Screen vs Vibrating Screen
• Grizzly Screen Maintenance Checklist
• Jaw Crusher CSS Setting Guide
• How to Prevent Screen Blinding

Product page:

• GELEN ITE Series Grizzly Vibrating Screens
• CK Series Jaw Crushers