ACK Asset Management LLC
In its 13F for Q1 2026 (holdings as of March 31, 2026, filed May 15, 2026), ACK Asset Management LLC reported 20 stock positions worth $801.1 million. Its top holding was Materion (MTRN) at 8.6% of the portfolio, followed by Advanced Drainage Systems (WMS, 6.7%) and Ats (ATS, 6.5%). Compared with Q4 2025, it opened 3 new positions, sold out of 6, added to 6 and reduced 1. The biggest buy was a new position in Littelfuse (LFUS) and the biggest sale an exit from Enersys (ENS).
- Most Recent 13F
- Q2 2026
- Location
- GREENWICH, CT
- CIK
- 0001510940
- Portfolio Value
- $801.1M (Q1 2026)
- SEC Filing
- 0001510940-26-000004 ↗ filed May 15, 2026
Holdings Value
Holdings 20 stocks · $801.1M
| MTRN Materion Corp. | 8.57% | 474,800 | $68.7M | No change |
| WMS Advanced Drainage Systems Inc. | 6.68% | 390,000 | $53.5M | No change |
| ATS Ats Corp. | 6.50% | 1,846,196 | $52.1M | No change |
| ROG Rogers Corp. | 6.36% | 475,000 | $51.0M | Add +8.8% |
| HLIO Helios Technologies Inc. | 6.30% | 780,378 | $50.5M | No change |
| LFUS Littelfuse Inc. | 5.72% | 135,000 | $45.8M | New |
| CNM Core & Main Inc. Class A | 5.55% | 900,000 | $44.5M | No change |
| NOVT Novanta Inc. | 5.53% | 375,000 | $44.3M | No change |
| SITE Siteone Landscape Supply Inc. | 5.48% | 330,000 | $43.9M | No change |
| ASTE Astec Industries Inc. | 5.29% | 786,500 | $42.3M | No change |
| JHX James Hardie Ind PLC | 4.96% | 2,100,000 | $39.8M | No change |
| DXPE DXP Enterprises Inc. | 4.53% | 260,000 | $36.3M | Add +8.3% |
| CDNL Cardinal Infrastructure GR-A | 4.33% | 874,000 | $34.7M | Add +3.5% |
| EXP Eagle Materials Inc. | 3.90% | 165,000 | $31.3M | No change |
| MBC Masterbrand Inc. | 3.84% | 3,700,000 | $30.7M | Add +60.9% |
| GVA Granite Construction Inc. | 3.74% | 250,000 | $30.0M | Reduce -50.0% |
| CTS CTS Corp. | 3.48% | 584,000 | $27.9M | New |
| SWIM Latham Group Inc. | 3.46% | 5,160,000 | $27.7M | New |
| MTASF Montana Aerospace AG filed as AERO-SWX | 3.35% | 830,000 | $26.8M | Add +436.0% |
| CLFD Clearfield Inc. | 2.43% | 735,200 | $19.5M | Add +17.6% |
Portfolio Sells Q4 2025 → Q1 2026
| ENS Enersys | Sold out | 0.00% | −5.61 |
| ATRO Astronics Corp. | Sold out | 0.00% | −4.07 |
| AIN Albany Intl Corp. Class A | Sold out | 0.00% | −3.82 |
| APOG Apogee Enterprises Inc. | Sold out | 0.00% | −3.72 |
| GVA Granite Construction Inc. | Reduce -50.0% | 3.74% | −3.50 |
| ERII Energy Recovery Inc. | Sold out | 0.00% | −1.15 |
| CTOS Custom Truck One Source Inc. | Sold out | 0.00% | −0.58 |
Portfolio Buys Q4 2025 → Q1 2026
| LFUS Littelfuse Inc. | New | 5.72% | +5.72 |
| CTS CTS Corp. | New | 3.48% | +3.48 |
| SWIM Latham Group Inc. | New | 3.46% | +3.46 |
| MTASF Montana Aerospace AG | Add +436.0% | 3.35% | +2.65 |
| CDNL Cardinal Infrastructure GR-A | Add +3.5% | 4.33% | +1.76 |
| ROG Rogers Corp. | Add +8.8% | 6.36% | +1.34 |
| DXPE DXP Enterprises Inc. | Add +8.3% | 4.53% | +1.23 |
| MBC Masterbrand Inc. | Add +60.9% | 3.84% | +0.65 |
| CLFD Clearfield Inc. | Add +17.6% | 2.43% | +0.14 |
All Filings
| Quarter | Positions | 13F Reported Value | Top Holdings |
|---|---|---|---|
| Q2 2026 | 21 | $856.3M | WMS, HLIO, LFUS, JHX, GTX |
| Q1 2026 | 20 | $801.1M | MTRN, WMS, ATS, ROG, HLIO |
| Q4 2025 | 23 | $796.8M | MTRN, GVA, WMS, ATS, CNM |
| Q3 2025 | 20 | $799.1M | ENS, MTRN, GVA, ATRO, WMS |
| Q2 2025 | 21 | $761.4M | ATRO, ATS, DY, GVA, ENS |
| Q1 2025 | 20 | $609.0M | DY, ENS, MTZ, ATS, ATRO |
| Q4 2024 | 22 | $746.4M | DY, MTZ, ATS, ENS, ROG |
| Q3 2024 | 18 | $809.2M | DY, MTZ, ENS, ROG, ATS |
| Q2 2024 | 19 | $810.3M | DY, MTZ, ENS, ROG, CNM |
| Q1 2024 | 20 | $858.3M | CNM, DY, ATKR, MTZ, ENS |