13F Portfolios

ACK Asset Management LLC 13F: Portfolio & Holdings

ACK Asset Management LLC (SEC CIK 0001510940) reported 20 positions with a combined market value of $0.8 billion in its most recent SEC Form 13F-HR filing (as of Q1 2026). The Greenwich-based hedge fund has a Industrials sector tilt, which represents 55.2% of its exposure.

Its largest holdings are Mtrn (MTRN) at 8.6%, Wms (WMS) at 6.7%, and Ats (ATS) at 6.5%.

The largest new position was Lfus (LFUS) at 5.7% of the portfolio. See the fund’s full Q1 2026 buys, sells, and portfolio changes →

Based on published SEC 13F filings, ACK Asset Management's closest peer funds by portfolio overlap are Mason Capital Management LLC (75.5%), Camrose Capital Investment Partners LLP (14.7%), and Hill City Capital, LP (13.6%).

13F AUM
$0.8B
Equity Positions
20
Top-10 Concentration
62.0%
Largest Sector · 55.2%
Industrials
Longest-Held Position · 31 qtrs
ENS
Median Holding Period
1 Qtrs

What are ACK Asset Management’s largest 13F holdings as of Q1 2026?

Largest 13F positions disclosed by ACK Asset Management, ranked by portfolio weight. Full multi-quarter history and the broader institutional holder base for each ticker linked per row.

Top 10 disclosed equity positions for ACK Asset Management in Q1 2026 — ranked by portfolio weight; share count and market value sourced from SEC Form 13F-HR filings.
# Issuer Ticker Sector Weight Position Value Detail
1 MTRN MTRN Basic Materials 8.6% $68.7M Position History All Holders
2 WMS WMS Industrials 6.7% $53.5M Position History All Holders
3 ATS ATS Industrials 6.5% $52.1M Position History All Holders
4 ROG ROG Technology 6.4% $51.0M Position History All Holders
5 HLIO HLIO Industrials 6.3% $50.5M Position History All Holders
6 LFUS NEW LFUS Technology 5.7% $45.8M Position History All Holders
7 CORE & MAIN INC CNM Industrials 5.5% $44.5M Position History All Holders
8 NOVANTA NOVT Technology 5.5% $44.3M Position History All Holders
9 SITEONE LANDSCAPE SUPPLY INC SITE Industrials 5.5% $43.9M Position History All Holders
10 ASTE ASTE Industrials 5.3% $42.3M Position History All Holders

View ACK Asset Management's Q1 2026 portfolio changes and trading report →

Latest

Portfolio composition

Sectors, concentrations, and a tap-through treemap of every position in the fund's latest 13F.

Allocation by stock20 positions · click any tile for institutional holders
Allocation by sector4 sectors · same palette as the stock tiles

Holding period analytics

Distribution of holding periods for all 551 stocks the fund has ever held (up to selected quarter):

Which Funds Hold a Similar Portfolio to ACK Asset Management?

Ranked by percentage of the peer fund's 13F equity portfolio that overlaps with ACK Asset Management's positions in Q1 2026.

Funds with the most portfolio overlap with ACK Asset Management in Q1 2026 — Ranked by overlap percentage
# Fund Shared Positions Overlap %
1 Mason Capital Management LLC 1 75.5%
2 Camrose Capital Investment Partners LLP 1 14.7%
3 Hill City Capital, LP 5 13.6%
4 Coliseum Capital Management, LLC 1 8.6%
5 Impactive Capital LP 1 8.5%
6 RDST Capital LLC 1 5.9%
7 Forest Avenue Capital Management LP 1 5.6%
8 D1 Capital Partners L.P. 1 4.8%
9 Pertento Partners LLP 1 4.4%
10 59 North Capital Management, LP 1 4.2%

How Has ACK Asset Management's AUM Changed Over Time?

Quarterly 13F-reported AUM for ACK Asset Management, derived from aggregate reported position market values disclosed to the U.S. SEC.

Methodology & FAQ

How We Track ACK Asset Management Holdings

Our data is systematically aggregated directly from quarterly Form 13F-HR disclosures submitted to the U.S. Securities and Exchange Commission (SEC).

  • Who Must File (Reporting Threshold): This dataset includes filings from U.S. institutional investment managers, hedge funds, mutual funds, university endowments, and family offices managing at least $100 million in Section 13(f) securities (including equities, options, convertibles, ETFs, and warrants).
  • What is Included (Data Scope): By regulation, 13F filings include long positions in U.S. exchange-listed stocks, ETFs, shares of closed-end investment companies, and convertible debt, as defined in the SEC's official Section 13(f) securities list . For listed options (calls/puts) the reported value is based on the notional value.
  • Portfolio Weight Explained (Metric Definition): “Portfolio Weight” shows how much of a fund's total reported 13F portfolio value (excluding listed options) is allocated to a specific position on the reporting date.
  • How to Use This Data (Interpretation): Quarter-over-quarter changes in shares and portfolio weight reflect a combination of active trading and market price movements. These are descriptive metrics of fund allocation, not explicit buy or sell signals.
What does ACK Asset Management's 13F filing disclose about their portfolio?

A Form 13F-HR filed by ACK Asset Management with the U.S. SEC discloses all long positions in Section 13(f) securities — U.S.-listed equities, ETFs, closed-end funds, and listed put/call options — held at quarter-end with a market value of at least $200,000 or 10,000 or more shares. Pactolio aggregates these filings to surface the manager’s reported portfolio weights, share counts, and quarter-over-quarter portfolio changes in a structured format. The filing represents a point-in-time snapshot of disclosed long-side exposure, not a real-time or complete view of the fund’s total book.

How do you measure conviction in ACK Asset Management's portfolio allocations?

Conviction is measured by portfolio weight — the percentage of ACK Asset Management’s total reported 13F market value allocated to a given position — rather than by absolute share count or dollar value alone. A position representing a disproportionately large share of the fund’s disclosed book signals high-conviction allocation, regardless of whether it ranks among the fund’s largest absolute holdings.

What is excluded from ACK Asset Management's 13F — short positions, swaps, and derivatives?

SEC Form 13F requires disclosure of long positions only. Specifically excluded are: short interest, total return swaps, credit default swaps, and all OTC derivatives — none of which appear in 13F filings regardless of position size. Listed put and call options must be disclosed but are excluded from portfolio weight calculations on this platform so that reported weights reflect direct equity exposure and remain comparable across filers. This means ACK Asset Management’s 13F represents the reported long book, which may differ materially from its net economic exposure.

When is ACK Asset Management's 13F data available, and how large is the reporting lag?

Investment managers must submit Form 13F within 45 calendar days of each quarter-end (the T+45 deadline). Pactolio ingests filings directly from SEC EDGAR as they are published — managers who file early appear in our system before the deadline, while late filers are captured on their actual filing date. The quarter label shown at the top of this page reflects the most recently processed 13F cycle for ACK Asset Management. The inherent reporting lag means the data always reflects positions as of the prior quarter-end, not current holdings.

Who must file a Form 13F with the SEC, and does ACK Asset Management qualify?

Under SEC Rule 13f-1, any investment manager — including hedge funds, family offices, registered investment advisers, pension funds, and university endowments — that exercises investment discretion over $100 million or more in Section 13(f) securities at any point during a calendar year must file Form 13F for that year. ACK Asset Management meets this threshold, which is why its holdings are publicly disclosed and accessible on this platform. The $100 million threshold is evaluated on a rolling basis, meaning new filers can enter and existing filers can exit the disclosure regime as AUM crosses that boundary.